ELEMENTS OF CHEMISTRY, 



FOR THE USE OE 



SCHOOLS ANB ACADEMIES, 



COMPRlSIIfG 



THE PRINCIPAL PART OF 



FOR THE USE OF PUPILS OF MECHANICS INSTITUTIONS, 

BY ANDREW FYFE, M. D. F. R. S. E. 

Lecturer on Chemistry to the Edinburgh School of Arta. 



WITH ADDITION'S AND ALTERATIONS 

BY JOHN W. WEBSTER, M. D. 

Erving Professor of Chemistry in Harvard University. 



WITHDRAWN 
BOM AMI 



BOSTON J 

PUBLISHED BY RICHARDSON AND LORD. 

J. H. A. FROST, PRINTER. 

1827. 



# 




DISTEICt OF MASSACHUSETTS-to wit. 

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BE n- REMEMBERED That on the twenty-first day a^^^^^^^ 
to the fifty-second y«ar of the Independence of the Umtea^^ ^^.^ ^^^ ^^ 

K^Torth^e!i2>tw'hl'^^^Sy°^^^^^^^^^^^ 



to wit : 



'.:tlements of Chemistry fo. the «se of Scho^^ 
principal part of aManual of Chemistry for the use otpupus^ ^^ ^^^ Edinburgh 
Iroollf^ir "v^Hk^adLL^and^^^^^^^^ W.^ Webster, M. D. 

Irving Pt'ofror of Chemistry in Harvard U--' ^ ^„,i,„, .. ^ ^ct 

In conformity to the f * "f *e Co^- f f^^^ Yhe' Copiefo'f Maps, Charts and 
for the Encouragement of Learning, by ^^^^^"?^p„-,:„g during the times therein 
Books, to the Althors and Proprietors o^^^^^^^ 

mentioned -and also to an Act entitled An Ac^^^^^^^ ^^^ ^ .^^ of Maps. 

An Act for the Encouragement «J ,^|Xiltor J of such Copies during the times 
Charts and Books to the Authors and Proprie^^^^ P ^^^ of desigmng, 

therein mentioned; ^^^ extending the bene^^^^^ ^ ^^^jg^ 

.-engraving and etching historical and '>therprmts. ofMassachtcscttT. 



ADVERTISEMENT. 



At the repeated request of several instructers, an 
abridgment of the " Manual of Chemistry^^ used as a 
text book in this University, had been commenced 
when Dr Fyfe's ^' ManuaP^ was received. His 
work was found to be so well calculated for begin- 
ners, that it was thought a more acceptable service 
might be rendered by republishing the most practical^ 
part of it, with some alterations and additions. The 
present work therefore is to be considered as chiefly 
consisting of Dr Fyfe's Manual. The first part is 
an abridgement from the " Manual on the basis of 
Brande,'^ from Dr Henry's Elements and Dr Paris' 
Medical Chemistry. In the appendix have been 
introduced directions for using Dr Ure's Alkalime- 
ter, and in several places in the text more full and 
practical observations have been substituted for those. 
of Dr F^yfe. 

Several pages having been printed before Dr Fyfe's 
work was received, the title which had been already 
adopted for the abridgement, was continued. 

J. W. W, 

Harvard University, i 
Nov. 14tb, 1827. \ 



PREFACE 
TO DR FIFE'S MANUAL. 



In compiling a work on Chemistry, for the use 
of pupils of Mechanics' Institutions, and who of 
course have not had the benefit of a Classical Educa- 
tion, I have not only studiously avoided the most 
abstruse parts of the science, but I have all along 
' endeavoured to explain its laws and operations in 
language as simple as the nature of the subject will 
admit. When I have been obliged to make use of 
technical expressions, I have taken care to explain 
them, and to give their origin. My reason for giv- 
ing the Greek words, from vvhich many of these are 
derived, not in Greek characters, will appear evident. 
I have endeavoured to elucidate the different facts 
by experiments which it is to be hoped will be easily 
understood ; and to make them still more intelligi- 
ble, I have had recourse to figures. These, I have no 
doubt, may to some appear to be too often repeated ; 
but I would rather be accused of repetition, in this 
respect, than of want of perspicuity. 

With respect to the arrangement, I have adopted 
that which I have all along followed in my lectures ; 



VI preface" 

it IS that long ago recommended by Dr Black, and 
which, even yet, with all the improvements that the 
science has experienced, is, with a slight modifica-- 
tion, 1 think, the best, both for a Lecturer and an 
Author. An Appendix is given, containing articles 
which it was thought advisable not to introduce into 
the body of the Work; and in addition to this, there 
is also a List of books, in which are discussed at full 
length the different articles treated of in the Work> 

Edinburgh, > 
July, 1826. S 



CONTENTS. 



Tage 

properties of Matter, - - - 13 

Attraction, - - - - 15 

Contiguous, - - - '•SI 

Cohesive, - - 21 

Chemical, - - - 27 

J Changes produced by, - - 29 

Solution, - - - - •* 31 

Distillation, - - - -^ 34 

Crystallization, - - . 3g 

Elective affinity, - - - 46 

Double, - - - 51 

Pov^'ers modifying affinity, - - - 52 

Tests, . - - - 55 

Atomic theory, - - '■50 



Heat, 



68 



-, Effects of, - - » . 59 

Expansion, - - - - 59 

Fluidity, - - - - 71 

Evaporation, - , - 75 

Incandescence, ... 84 

-, Communication of, - - 83 

-, Quantity of, in Bodies, - -• - 103 

-, Sources of, - - - - 106 



via CONTENTS. 

Page 

Light, - - -r - 120 

Atmosphere, - - - - - 128 

Nomenclature, - - - - 133 

Oxygen, - - a. - . - - 139 

Nitrogen, » - . - - 142 

Hydrogen, ... . 145 

Water, - - - - 147 

Charcoal, - - - - 152 

Carburetted Hydrogen, - - - 155 

Olefiant gas, - - - - 159 

Chlorine, ' - - - - 161 

Sulphur, - - - - - - 163 

Acids, - - - • 166 

Nitric, - .... 167 

Carbonic, - - - - - 169 

Muriatic, - - - - 172 

Sulphuric, - - - - - 173 

Alkalies, - - ^ - - 176 

Potassa, - - - - 177 

Soda, » - - - - 177 

Ammonia, - - - . 179 

Neutral Salts, - - - - 181 

Nitrate of Potassa, - - - 1 83 

Carbonate of Potassa, - - - 191 

Carbonate of Soda, ... 192 

Muriate of Soda, - - ^ ^ I95 

Muriate of Ammonia, - - - 108 

Chlorate of Potassa, - ^ - 201 

Earths, - - - - . 2Q4' 

Lime, - - - - - 205 

Alumina, - - . . . 224 

Silica, - - - - - 226 



CONTENTS. 

ix 

Page 

Metals, ----- 236 

Iron, - - - .242 

Copper, . - - .251 

Lead, - . . .254 

Tin, 257 

Zinc, - - - - ^^^ 

Mercury, . - - - 264 

Gold, - . - - 268 

Silver, . - - - 273 

Platinum, - - - " ^80 

Manganese, * - " " 28^ 

Bismuth, . - - - 284 

Cobalt, - - - - - 285 

Arsenic, - - - 287 

Antimony, - - - - 289 

Vegetables, - - - " - 291 

Vinous Fermentation, - - - 291 

Alcohol, - - . . 299 

Acetous Fermentation, - - ^^^ 

Putrefaction - - - - 302 

Vegetable Principles, - - - ^07 

Sugar, - - .... 307 

Gum, ... 309 

Starch, - - - 310 

Wax, - " - 313 

Oils, - . . - - 314 

Fixed, - - - - 314 

Volatile, .- - - - 320 

Resins, ... .322 

Tar, . - , - 324 

Caoutchouc, - - - - 325 

Tannin, - - - • 327 



CONTENTS. 



Animal Substances, 

Gelatin, 

Albumen, 

Milk, 

Bile, 
Colouring Matter, 

Dyeing, 
Electricity, 
Galvanism, 



Pagt 

328 
329 
338 
339 
342 
342 
346 
350 
359 



ERRATA. 

Page 94, line 22 before " charcoal'' insert 
"• ignited '^ 

115, for Exp. 40, read Exp. 5Q. 

153 line 25 for '* powder or charcoal'^ read 

*" powder of charcoal/^ 

271, line 26 for i read j\. 



ELEMENTS OF CHEMISTRY. 



Most of the substances belonging to our globe 
are constantly undergoing alterations in sensible 
qualities, and one variety of matter becomes as 
it were, transmuted into another. Such changes, 
whether natural or artificial, whether slowly or 
rapidly performed, are called chemical, and it is the 
object of chemistry to ascertain the causes of all 
phenomena of this kind, and to discover the laws by 
which they are governed. 

As chemistry investigates the changes that affect 
the constitution of material substances it will be 
necessary to acquire some previous knowledge of 
matter and its properties. 

1 PROPERTIES OF MATTER. 

Whatever is capable of acting upon our senses 
has been called matter; or we may define matter 
as whatever occupies space, or which has leqgth, 
breadth and thickness. The different portions of 
matter are called bodies. 

Some of the essential or general properties of 
matter are Extension, Divisibility, Impenetrability, 
Porosity, and the power of attracting or being at" 
tracted. 

There are also secondary or contingent properties, 
such as Solidity, Fluidity, Elasticity, &c. which, by 
their combination with the general properties, con- 
stitute the condition or state of bodies. It is by 
gaining or losing some of these secondary properties 
that bodies change their state; thus, water is seen in 
a solid state, and in the state of steam having acquir- 
ed elasticity, still it is the same body. 
% 



14 ELEMENTS OP CHEMISTRY. 

By the mecha7iical properties of matter we mean 
those which are obvious upon any of the mechanical 
operations of breaking, weighing, measuring, or the 
like, without any regard to the composition of the 
body under examination; thus the general Tnechani- 
cal effects of water will be the same whether it be 
taken from a river or a spring, but if its composition 
be examined chemically it may be found to vary. 

Divisibility is a property which belongs to every 
substance which can be brought under the cog- 
nizance of our senses. To what extent a body may 
be divided before we arrive at its simple elementary 
atoms, we shall probably never be able to conjecture. 
If a piece of marble, or any other substance be re- 
duced to the finest powder its original particles, or 
atoms, will not be bruised or affected, and if the 
powder be examined by a microscope each grain 
will be found a solid stone, similar in appearance to 
the block from which it was broken. A single 
grain of blue vitriol (sulphate of copper) vv'ill com- 
municate colour to five gallons of water, in which 
case the copper must be divided several millions of 
times, and yet each drop of the liquid may contain 
as many coloured particles. A single grain of musk 
has been known to perfume a large room for the 
space of twenty years. 

Porosity is a property belonging to all bodies 
with which we are acquainted. Upon the extent of 
this, the relative densities of bodies depend ; tlius, if 
it be supposed that a million particles of gold are 
contained in a cubic inch of that metal, 500,000 
particles of iron might also be capable of occupying 
the same space, or 100,000 particles of wood. In 
the iron and wood there must, therefore, be many 
more interstices or pores ^ than in the gold, and of 
course, the gold will be the heaviest or most dense. 
This superior density and weight arises therefore 
from a greater number of the individual atoms of 
gold being forced into the same space. 



ATTRACTION. 15 

The existence of porosity in every species of mat- 
ter which can be subjected to our senses is proved 
by the universal compressibility of bodies. There 
is no substance, however dense, that may not be 
made to occupy less space. 

Impenetrability ; the existence of this property 
necessarily follows from the fact, that no two bodies 
can occupy the same place in the same precise in- 
stant of time. 

The atoms of matter, are impenetrably hard ; a 
property which ensures eternity to the works of 
nature; for although to the superficial observer, mat- 
ter may in many instances seem to disappear, yet 
chemistry proves that it is incapable of annihilation, 
and that the original atoms, still exist, although by 
change of arrangement they are made to assume 
different states, 

ATTRACTION. 

Attraction may be defined, that force which causes 
distant bodies to approach each other, while it pre- 
serves those which are contiguous, in apparent con- 
tact. 

It may therefore be considered as acting betvv^een 
large masses of m.atter at sensihle distances, when it 
is termed the attraction of gravitation ; or as operat- 
ing between the minute atoms of bodies, at insensi- 
ble distances, when it is denominated contiguous 
attraction. This latter force admits of a further 
distinction, as it may act between similar or dissimi- 
lar particles of matter. In the former case, as for 
instance, where it operates between the particles of 
marble it is termed the attraction of aggregation or 
cohesion, since the effect of it is to produce an aggre- 
gate or mass ; but in the latter case, where it brings 
together particles perfectly dissimilar in nature as 
those of an acid and an alkali, it is termed chemical 
affinity, and the result is a new body. 



16 ELEMENTS OF CHEMISTRY. 

The following tabular arrangement exhibits the 
dififerent species of attraction with which the chemi- 
cal student should become acquainted. 



-- >^.— ^ 


ATTRACTION. 


Remote. 


Contiguous. 


Gravitation. 


r" 'a r" ' " -' ' * 

Acting between Acting between 
similar particles. dissimilar particles. 



Cohesion. Chemical affinity. 



..^... 



Single, Double. 

Gravitation. This force acts upon bodies remotely 
situated with respect to each other; it maintains the 
moon in her orbit, and upholds the circulation of the 
whole system of planets around the sun, and causes 
every body upon our globe to fall towards its centre, 
or in a line perpendicular to its surface. 

The quantity of the bodies we employ in our 
various operations is most accurately determined by 
their force of gravitation, or weight. Two kinds of 
weight are in common use,, viz. Troy and Avoirdu- 
pois — the former is used in the valuation of gold, 
silver and platinum, and in the composition of medi- 
cines; the latter is employed in merchandize. The 
following table exhibits the manner in which the 
pound is divided, 

TROY WEIGHT. 

Pounds = Ounces = Drachms = Scruples = Grains. 

1 = 12 = 96 = 228 = 5760 

1 == 8 = 24 = 480 

1 = 3 == 60 

1 == 20 

AVOIRDUPOIS WEIGHT. 
Pound Ounces Drachms Grains. 
1 = 16 = 256 = 7000 
1 = 16 = 437,5 

1 = 27,975 

The pound is usually expressed by the sign ife and 
its subdivisions by the following symbols, viz. 




SPECIFIC GRAVITY, 17 

The annexed figure represents an ounce; 

by omitting the upper part and commencing 

at A, a drachm ; and the lower portion, b, 

c, a scruple. A grain is expressed by the 

^ simple contraction gr. 

In chemical experiments it will be found very 
convenient to admit no more than one description of 
weight, the grain. 

The most convenient set of weights for the che- 
mist, is one that corresponds w'ith our numerical 
system, thus 1000, 900, SOO, 700 grains, &c. down 
to Y%ths of a grain. With these w^e can always have 
the same number of w^eights in the scales as there 
are figures in the numbers expressing the weights in 
grains: thus 742,5 grains will be weighed by the 
weights 700, 40, 2, and 5_ths.* 

When weighing powders, it is best not to lay 
them on the scale pan, but upon some interposed sub- 
stance ; two slips of glass, or two watch glasses of 
equal weight may be used ; they have the advantage 
of generally resisting any chemical action of the pow- 
der, and of being easil}^ kept clean : or hot pressed 
wove paper may be used, the edges being cut, not 
torn, as the powder in the latter case would adhere 
to the rough edges when passing over them. 

The comparative weight of a body has been term- 
ed its specific gravity, its w^eight being compared 
WMth that of another whose magnitude is the same, 
and for the accurate expression of such a relative 
quantity it became necessary to fix upon some sub- 
stance as a standard. Distilled water at the tempera- 
ture of 60° is taken as the unit of comparison, or the 
datum from which all calculations of specific gravity 
should proceed, and is called 1,000; thus if a cubic 
inch of any solid body were found to be double the 
weight of a cubic inch of water such body would be 

* For measuring fluids, glass measures are used ; these may be of different sizes 
and graduated into cubic inches, or ounce measures equal to the bulk of an ounce 
of water. By the late parliamentary standa d of G. Britain, the pint contain? 8T5f{ 
grs. of water at 62'-^ F. and the cubicinch 252.458 srs. 



IS ELEMENTS OF CHEMISTRY. 

specifically heavier than water in the proportion of 
two to one, and its specific gravity would accordingly 
be set down thus, 2. If again its weight were equal 
to that of two and a half cubic inches of water it 
would be specifically heavier than water in the 
proportion of two and a half, to one ; and its spe- 
cific gravity would in that case be set down as 2,5 ; 
the fractional parts being always expressed by deci- 
mals. 

During the various changes which bodies undergo 
by combination with each other, a diminution or 
increase in their specific gravities is not the least 
remarkable or important : in some cases they are 
diminished, and in others increased. Thus alcohol 
and water, when mixed, will have a volume less than 
the sum of their respective volumes. 

The instrument by which the specific gravity of 
bodies is ascertained is called the Hydrostatic Bal- 
ance. 

B, C, D, is a balance ; — E, a (T^ 

glass jar about six inches in || 

height, which contains distilled < vJL-jJ I^^ 
or rain water. The mode of h j TTj, 

using this instrument is as fol- / \ n <^^ 
lows : — Let the solid, say for /^ J ^^ 
example a piece of common ^^^dS? fe^E 
brimstone, whose specific gi^a-^^ jj Ic^^^iX 

vity is to be ascertained, ^^ ^^— — — rr^ 

suspended by a fine hair, or fila- \l ^ 1 

tnent of raw silk, from the scale Cjand weighed in air; 
suppose it to weigh 12 grains; let it next, still sus- 
pended to the balance, be immersed in the distilled 
water of the temperature of 60° Fah^ as represented 
in the annexed figure ; the scale containing the 
weight will now preponderate ; add therefore to the 
scalej^ C, as many grain weights as may be necessary 
to restore the equilibrium ; suppose that six grains 
are necessary for this purpose, then this will indicate 
the amount of the weight lost in the water. We 



GRAVITY BOTTLE. 19 

must now divide the real weight of the body in air, 
viz. 12 grains, by this loss, 6 grains, which gives us 
2 as the specific gravity of the body under examina- 
tion. 

Care should be taken that no air bubbles are 
attached to the substance, for they would have a 
tendency to buoy it up ; should they occur they may 
be easily detached by means of a hair pencil. 

The most convenient method of asceriaining the 
specific gravity of fluids is by means of a Gravity 
bottle. It is a bottle with a slender neck, 



^ furnished with a ground conical stopper in 
^^ (jj the side of which there is a notch by which 
the operator is enabled to put in the stopper 
after the bottle has been completely filled, 
the redundant fluid escaping through this 
\ groove. Unless such a contrivance were 
J adopted it would be difficult to fill the bottle 
" ^ without enclosing some bubbles of air. 
The weight of this bottle, with its stopper must 
be carefully noted in grains, or a weight may be at 
once procured, that shall always serve as a counter- 
poise. The bottle is then to be filled with distilled 
water at 60° Fah, and its weight in grains carefully 
noted. In taking the specific gravity of any other 
fluid we have only to fill the gravity bottle with it, 
and then to ascertain the exact weight in grains, 
which if it be divided by the weight of the water 
contained in the bottle will give a quotient which 
will be the specific gravity of the fluid in question. 
Suppose for example we wish to find the specific 
gravity of a solution of the carbonate of potassa^ 
and that the bottle in which the experiment is to be 
made contains exactly 1750 grains of the solution, 
and that the same quantity of water weighs no more 
than 1425 grains. In this case, we have only to 
divide the greater by the less sum, and the quo- 
tient 1,222 will be the specific gravity required. 
For conducting this experiment with greater facility 



20 ELEMENTS OF CHEMISTRY. 

a gravity bottle is now usually sold under the name 
of a " Thousand grain bottle,^' together with a 
weight which is an exact counterpoise for it when 
filled with distilled water at 60^ Fah. This instru- 
ment consequently does not require the aid of any 
computation, but is simply filled with the fluid to be 
examined and placed in one scale of the balance 
while its counterpoise is placed in the other. If the 
contained fluid be lighter than water it will appear 
deficient in weight and as many grains must be 
added ^o the scale that contains it as may be suflicient 
to restore the balance ; but should the fluid be heavier 
than water, the bottle will preponderate, and weights 
must be put in the opposite scale, when their amount 
hein^ positive^ must be added to that of the standard.* 
Another mode of estimating the specific gravity 
of fluids, is founded upon the same proposition as 
that to which the Hjdrostatical balance above de- 
scribed owes its utility, viz. that a body when 
weighed in any liquid^ loses just so much of its 
weight as is equivalent to that of the same bulk 
of the liquid. It is clear therefore, that, if we are 
required to compare the specific gravities of two 
liquids, we have only to take some solid body 
heavier than water, and to observe kow much weight 
it loses in each, and we shall thus acquire the com- 
parative weight of the same bulk, which is as the 
specific gravities of the fluids respectively ; but as 
the specific gravity of water is not in such a case 
expressed by unity, we must say 

Jis the loss of weight in water 

Is to the loss of weight in the fluids 

So is Unity 

To a fourth Proportional. 

* For example, if the bottle were filled with Sulphuric yEther, it would require 
739 grains to be placed in the same scale to restore tiie balance, and consequently, 
its specific gravity would be expressed tlms 0.739. Kad it been fdled with sea water, 
which is rather more dense than that which is distilled, 26 hundredths, or rather 
better than a quarter of a grain must have been added in the opposite scale, and 
which, as already explained, must be added to the standard 1,000 to express the spe- 
citic gravity of such water, which W(m!d bo slated thus 1.026. Sulphuric acid again, 
being still heavier, would, in like manner, require 875 grains, and must according^ 
be expressed as 1.875. 



COHESION. 21 

Or divide the loss of weight in the other fluid by 
the loss of weight in the water, and the quotient 
will express the specific gravity of the former. 

A ball, or pear-shaped lump of glass, sus- 
pended by a fine platinum wire, as represent- 
ed in the annexed figure, is usually sold for 
the purpose of the above experiment ; and, 
were it ground to such a size as to lose 
exactly a thousand or ten thousand grains in 
distilled water, no computation would be re- 
quired 5 its loss of weight by immersion, indi- 
cating at once the specific gravity of the 
fluid. 

CONTIGUOUS ATTRACTION. 

We have hitherto only considered attraction as 
exerted aver masses of matter, at seiisible distances; 
we have now to examine its influence over the 
minute atoms of bodies placed with respect to each 
other at insensible distances. Where these atoms 
are similar in their nature, the result of this power 
is simple ag2;regation ; but where dissim^ilar it gives 
origin to new and infinitely varied productions. 

COHESION. 

Synon. Attraction of Aggregation — Cohesive Affini- 
ty — Corpuscular Attraction — Homogeneous Affinity. 

It may be defined, that force or power by which 
particles or atoms of matter, of the same kind, 
attract each other, and produce an aggregate or 
mass. 

This force is exceedingly various in different 
bodies, and even in different states of the same body. 
In solids its force is exerted with the greatest inten- 
sity ; in liquids it acts with much less energy ; and 
in aeriform bodies it is doubtful if it exists at all : 
thus w^ater in a solid state has considerable cohesion^ 



22 ELEMENTS OF CHEMISTRY. 

which is much diminished when it becomes liquid, 
and is entirely destroyed. as soon as it is changed 
into vapour. 

The force of cohesion in solid bodies is measured 
by the weight necessary to break them, or rather to 
pull them asunder. 

In liquids the force of cohesion is demonstrated 
by the spherical figure which they assume, when 
suffered to form drops. The drop is spherical 
because each particle of the fluid exerts an equal 
force in every direction, drawing other particles 
towards it on every side, as far as its power extends. 
To the same cause is owing the property possessed 
by all liquids of remaining heaped up above the 
brims of the vessels which contain them. 

The force of cohesion varies in different liquids, 
as it does in different solids and hence the size of 
their respective drops must also vary. 

An important modification of this force occasions 
liquids to rise in small tubes, and as it is most con- 
spicuous when the width of the bore is so small as to 
resemble that of a hair, it has been called Capillary 
attraction. Capillary attraction is not confined to 
glass tubes, but is exerted among all substances 
which are perforated by pores or subdivided by 
fissures or interstices. It is this attraction, for in- 
stance, which causes water to rise in sponge, cloth, 
sand, &c. 

The force of cohesion is continually opposed to 
the action of chemical affinity; for the more strongly 
the particles of any body are united by this power, 
the less are they disposed to enter into combination 
with other bodies ; hence the mechanical operations 
of rasping, pounding, sifting, &c. 

Fulverizcition and trituration^ by which substan- 
ces are reduced to powder, are generally performed 
by means of pestles and mortars. The most useful 
mortars are those of porphyry and Wedge wood's 
ware. 



SIFTING — WASHING. 



23 




Levigation is a process similar to trituration ex- 
cept that the rubbing is assisted by the addition of a 
liquid in which the solid under operation is not 
soluble. Water or spirit is usually employed, and 
in some cases viscid and fatty matters, such as honey, 
lard, &c. The substance to be levigated is spread 
on a flat table of porphyry, or some other hard stone, 
as represented in the annexed figure and is then 

rubbed with a muller «, of 
the same materials, either 
of a pyramidal shape, or a 
portion of a large sphere. 
A thin spatula of ivory, 
^ ■ =^ horn, wood, or iron, is 

employed to collect the substance occasionally and 
bring it under the muller. 

Granulation is effected either by pouring the 
substance while in fusion into cold water, or by agi- 
tating it in a box. It is employed for dividing the 
metals, and phosphorus. 

Sifting is employed for the purpose of obtaining 
bodies in powder of an equal degree of fineness 
throughout. When very subtle materials are to be 
sifted, which are easily dispersed, or when the finer 
parts of the powder may be injurious to 
r-^^ the operator, a compound sieve should 
be used. It consists of a simple sieve, 
c, with a deeper rim; a lid, b covered 
with leather, and a receiver d having 
leather stretched across one end, and made 
sufiiciently wide to admit the lower por- 
tion of the sieve to enter and fit tightly 
within it. 

Elutriation or washing. By this operation we 
are enabled to procure powders of a greater and 
more uniform fineness, than by the sieve, but it can 
only be employed with such substances as are not 
acted upon by the liquid used. The powdered sub- 
stance is mixed and agitated with water^ or any 




24 



ELEMENTS OP CHEMISTRY. 



other convenient fluid, the liquor is allowed to 
settle for a few moments and is then decanted 
off;* the coarser powder remains at the bottom 
of the vessel, and the finer passes over with the 
liquid. 

Where it is desirable to avoid disturbing the sedi- 
ment, a liquid may be drawn off by means of a 
syphonA 



The inconvenience of applying the 
mouth to the extremity of the leg 
is prevented by the supplementary 
tube b. 



Filtration is an operation by means of which a 
fluid is mechanically separated from consistent par- 
ticles merely mixed with it. A Jiltre is a species of 
very fine sieve which is permeable only to the par- 
ticles of fluids. 




* In performing this operation, especially if the fluid be decanted from a "wide 
mouthed -vessel, a glass rod should be applied to the rim which will have the effect 
of directing the hquor in a regular stream. 

t The Syphon is any bent tube having its two legs either of equal, or unequal 
length, as here represented. If the two legs of the 
tube be of equal length, and it be filled with water, 
and then inverted with the two open ends down- 
wards, and held level in that position, the water 
will remain suspended in it ; for the atmosphere 
will press equally on the surface of the water in 
each end and support them. But if, now, the 
Syphon be a little inclined to one side, or, if the 
legs be of unequal length, as above represented, 
which is the same thing, so that the orifice of 
one end b8 lower than that of the other ; then 
the equilibrium is destroyed, and the water will 
all descend out by the- lower end, if, and rise up 
in the higher. For, the air pressing equally, but 
the two ends weighing unequally, a motion must comnience where the power is 
greatest, and so continue till all the water has run out by the lower end. And if 
the shorter leg be immersed into a vessel of liquid, and the Syphon be set running as 
above, it will continue to run until all the water be exhausted, or, at least, as low as 
that end of the Syphon. Or it may be made to run without first filling the Syphon, 
as above described, by only inverting it, with its shorter leg in the liquid ; then with 
the mouth apphed to the lower orific, ?, sucking the air out, when the fluid will pre- 
sently follow, being forced up into the Syphon by the pressure of the air on the water 
in the 1 ' 




FILTRATION. 



26 




Flannel fillers are particularly eligible 
also where our object is to preserve the 
solid residue, but when the filtered 
liquor is the valuable product, linen is 
generally preferable, as it absorbs 
less of the fluid, which is thus obtain- 
ed also in a more limpid state. 

For smaller processes, and where it is essential 
to have the filters perfectly clean, unsized paper is 
substituted. A square piece of this paper, of a size 
pruportionate to the quantity of the substance to be 
filtered is taken and first doubled from corner to 
corner into a triangle, which by second doubling 
forms again a smaller triangle, and this when open- 
ed constitutes a paper cone, as here exhibited (Fig. 1) 
which is to be supported in a glass funnel (Fig. 2) 
before the liquor is poured into it. It is of advan- 
tage to introduce glass rods, pieces of straw, or 
quills, between the paper and funnel, to prevent 
them from adhering too closely ; for this reason 
ribbed (3) are preferable to plain funnels. 

3 




Very acrid liquors, such as acid^ and alkaline 
solutions, act too powerfully on the ordinary mate- 
rials of filters, and are accordingly filtered through 
strata of differently sized particles of siliceous mat- 
ter ; for this purpose, a glass funnel is filled with 
powdered quartz or flint glass ; a few of the larger 
pieces being placed in the neck, which are covered 



.( 



26 ELEMENTS OP CHEMISTRY. 

with the smaller fragments, the finest, or white sand, 
being placed over all. The liquid to be filtered is 
poured gently on the surface, and soon passes 
through it, leaving the impurities behind. The 
porosity of this filter, however retains much of the 
liquor; but it may be obtained by gently pouring on 
it an equal quantity of distilled water ; the liquor 
wnll then pass through, and the water will be retain- 
ed in its place. 

In many instances the first portions of fluid that 
pass through the filter are turbid, and require to be 
returned, until the pores of the filter are sufficiently 
obstructed to permit the most limpid part only of 
the liquor to pass. In cases where the solid residue 
is small, and it is requisite to collect the whole of it^ 
it is useful to have a small glass tube, drawn to a 
capillary point at one extremity, and having a 
bulb in its centre as represented in the margin 
By filling this with distilled water, and putting 
the large end into the mouth, the force of the 
breath can direct a small strong stream of water 
round the sides of the paper in the funnel, which 
will wash down to its bottom all the minute particles 
of solid matter lodged on its sides. 

The filtration of some liquids is assisted by heat ; 
in such cases a funnel with a double case may be 
constructed so as to hold boiling water. Where 
several filtrations are in progress at the same time, a 
stand will be found very convenient for the reception 
of the funnels. (See Manual^ ph iK.fig. 17.) 

Expression is a species of filtration, assisted by 
mechanical force. It is principally employed to 
obtain the juices of fresh vegetables, and the unctu- 
ous vegetable oils. The subject of the operation is 
first bruised, or coarsely ground, then enclosed in a 
hair-cloth bag, and subjected to violent pressure 
between the plates of a screw press. The bags should 
be nearly filled ; and the pressure should be gentle at 
firsts and gradually increased. 



CHEMICAL AFFINITY. 27 

Vegetables intended for this operation ought to be 
perfectly fresh, and freed from all impurities. In 
general, they should be expressed as soon as they 
are bruised. 

Fluids of different specific gravities, 
may be separated by means of the Sepa- 
rator!/. The vessel is first stopped at the 
bottom, and then filled with the mixed 
fluids, the heaviest of which gradually sub- 
sides into the narrow part below ; and 
when the cock, a, is opened and the stopper 
above a little loosened, it flows out, by 
which contrivance the lighter is easily 
obtained in a separate state. 




CHEMICAL AFFINITY. 

This species of attraction, like that of cohesion, 
is effective only at insensible distances; but it differs 
from the latter force, in being exerted between the 
particles, or atoms of bodies of different kinds, and 
in producing by its agency, not a mere aggregate 
possessed of the same properties as the separate 
parts, and differing only in its greater quantity or 
mass, but a new compound, in which the properties 
of the components have either wholly, or in part, 
disappeared, and been superseded by new qualities. 

Where two heterogeneous or dissimilar bodies, 
are placed within the sphere of each other^s attrac- 
tions, and form a direct union, the phenomenon is 
termed Combination, the substances so produced, a 
Compound, and the bodies from which it has been 
formed, its Constituent Principles^ or Component 
Parts. 

The process by which a compound body is resolv- 
ed into its constituent parts is in chemical language 
termed Analysis ; whereas that, by which a com-- 
pound is formed by combination, is denominated 
Syiithesis. And under these are comprehended 
the greater part of the operations of Chemistry. 



28 - ELEMENTS OP CHEMISTRY. 

That chemical affinity is effective only at insensi- 
ble distances may be demonstrated by the following 
experiments. 

Experiment 1. — Into a deep ale-glass, or glass jar, pour two 
fluid-drachms of a solution of the Subcarbonate of Potassa ( Liquor 
PotasscR Sub'Carbonalis^) diluted with about fourteen fluid- 
drachms of distilled water. Under this introduce, very cautious- 
ly, half a fluid-ounce of water holding a drachm of common salt 
in solution ; and again, under both these, one fluid-ounce of 
Sulphuric Acid which has been previously diluted with an equal 
quantity of water.* If this arrangement be carefully accomplish- 
ed, we shall perceive, notwithstanding the powerful attraction 
which subsists between the alkali and acid, that no action will 
take place ; because their particles are separated from each other 
by a thin stratum of brine ; as soon however, as this arrangement 
is disturbed by agitation, a brisk effervescence will commence, 
and a chemical combination take place* 

Exp. 2. — Take one grain of Chlorate of Potassa^ and half a grain 
of the Flowers of Sulphur^ mix them cautiously, and no action 
will ensue ; rub them, however, in a warm mortar, so as to bring 
the particles into nearer contact, and a smart detonating noise 
will be produced. Continue to rub the mixture hard and the 
reports will be frequently repeated, accompanied with vivid 
flashes of light, 

Exp. 3. — Mix a little Acetate of Lead with an equal quantity 
of Sulphate of Zinc^ both in fine powder ; stir them together 
with a piece of wood or glass, and no chemical change will be 
perceptible ; but if they be now rubbed together in a mortar, the 
two solids will operate upon each other, and a fluid will be 
produced. 

In many cases the necessary contiguity of the 
particles cannot be effected without the processes of 
solution and fusion ; thus, if we mix together, the 
powdered crystals of dry Tartaric acid, and Carbon- 
ate of Soda, no action will be perceived, but the 
moment water is added, and a solution thus effected^ 
they will act chemically upon each other, and a brisk 
effervescence will arise. 

In order to show that the result of chemical com- 
bination is the formation of a 7iew body, in which 
the properties of the components have either wholly, 
or in part, disappeared, and been superseded by 

* The delivery of these different fluids may be effected by the dropping tuho 
above described (26), or by means of a common glass tube open at each extremity, 
which, having been plunged in the liquid, must be withdrawn with the thumb closely 
applied to the upper orifice ; when by immersing it to the bottom of the jar, and theft 
removing the thumb, the fluid will be deposited in the manner required. 



EXPERIMENTS. 



29 



Others, numerous experiments might be related, but 
the following have been selected as being at once 
striking, and easy of performance. 

Exp. 4. — Two Odorous bodies produce a compound destitute of 
Odour, Water impregnated with Ammonia and Muriatic Acid^ 
are fluids of a very pungent odour ; they may be mixed in such 
proportions that a fluid will result entirely devoid of smell. 

Exp. 5. — Two Fluids produce a solid. Into a saturated solu- 
tion of Muriate of lime, let fall, gradually, concentrated Sulphu- 
ric acid ; a quantity of pungent vapour (^Muriatic acid gas and 
ivater) will immediately arise, and an almost solid compound 
(^Sulphate of lime) be produced. 

Exp. 6. — Two Solids produce a Fluid, This has been already 
exemplified by experiment 3 ; or we may triturate together equal 
parts of crystallized Nitrate of Amm^onia and Sulphate of Soda^ 
when the saline mixture will shortly assume the liquid form. 

Exp. 7. — Two Gases produce a Solid ; thus, when muriatic gas 
and ammoniacal gas are mingled together, they produce the solid 
salt called Sal Ammoniac^ or Muriate of Ammonia. Take two 
wine-glasses, into one put a small quantity of sal ammoniac in 
powder, and into the other a spoonful of common salt, add 
quicklime to the one, and sulphuric acid to the other ; from the 
former ammoniacal, from the latter muriatic gas, will be evolved. 
As soon as the two vessels are made to approach each other, the 
gases will intermingle and combine, and display the formation of 
a solid product, by the appearance of white fumes of great 
densitya thus, 




Exp* ^,-—Tivo colourless fluids produce a compound of a blue 
colour. Into a wine-glass, containing water, add a few drops of 
Prussiate of Potassa ; and into another, a little of the dilute solu- 
tion of Sulphate of Iron ; on mixing these two colourless liquids 
together, a bright deep blue colour will be instantly produced, 
which is ^^ Prussian JBlue,^'' — Or, 
3- 



30 ELEMENTS OP CHEMISTKr/ 

' Exp. O.—Introduce a solution of Prussiate of Potassa into oti# 
glass, and into a second, that of Nitrate of Bismuth ; on mixing 
together these liquids a yeliow compound will result. 

Exp. 10. — The same Vegetable infusion will yield three differ' 
ent colours^ on the addition of three colourless fluids. Pour boil- 
ing water upon a few slices of red cabbage, and, when coid^ 
decant the clear infusion ; distribute the liquor into three wine- 
glasses. To the first add a solution of Alum ; to the second, that 
of Potassa ; and to the third, a few drops of Muriatic acid. The 
liquid in the first glass will be thus made to assume Si purple^ that 
in the second, a bright green^ and that in the third, a beautiful 
crimson colour. 

Exp. 11. — Two blue liquids become red by combination. Pour 
a little Tincture of Litmu? into a wine-glass; and into another, 
some diluted Sulphate of Indigo ; and the compound will have a 
perfectly red colour. 

Exp. 12. — Two Corrosive substances produce a mild compounds 
If we add together Sulphuric Acid and Potassa, two highly caustic 
bodies, we shall produce Sulphate of Potassa, a mild aud almost 
tasteless compound. 

In cases of this kind where chemical combination: 
takes place, and the qualities of the component parts 
of a compound are no longer to be detected in it, the 
bodies combined are said to neutralize each other. 
Thus the potassa and sulphuric acid in the last expe- 
riment, in a separate state have peculiar properties ; 
the former converts the blue colour of vegetable 
infusions to green, the latter to red; but if we gradu- 
ally add the one to the other we shall obtain a liquid 
which will have neither the properties of the acid 
nor of the potassa, and which will no longer affect 
the vegetable colour. 

Exp. 13. — Infusible bodies form fusible Compounds, Thus, 
neither Clay, Silica, nor Lime, will melt singly, but when these 
three earths are mixed in due proportion, a highly fusible com- 
pound is the result. In the same manner. Bismuth, Lead, and 
Tin, when separately heated, require a comparatively high 
temperature to effect their fusion; whereas the alloy formed by 
their combination will melt m boiling water. 

The experiments above related illustrate the im- 
portant changes which bodies undergo by chemical 
combination with each other; but it does not neces- 
sarily follow that every compound is marked by an 
equally great change , in some cases of combination^ 



SOLTTTION. 31 

the resulting body will differ but little in appearance 
or qualities, from the ingredients of which it is com- 
posed. This fact is exemplified by the phenomena 
of Solution. 

By solution chemists understand a certain opera- 
tion, by which a solid body combines with a fluids 
in such a manner that the compound retains the form 
of a transparent d^nA permanent fluid ; the two being 
inseparable by any mechanical means. When a 
lump of salt or sugar is thrown into water it disap- 
pears, and the liquid becomes a solution of salt or 
sugar. 

Solution is to be distinguished from simple mix- 
ture^ or mere mechanical diffusion. 

Exp. 14. — Thus if we diffuse a quantity of magnesia in water, 
a white turbid mixture will be formed, which on being left at rest 
some time will deposite the magnesia, and the water will regain 
its transparency. This is an instance of mere mixture. If how- 
ever, to the turbid liquid a few drops of nitric acid be added, it 
will become transparent, and the magnesia can no longer be 
separated by any mechanical process or by rest ; the nitric acid 
having combined with the magnesia forms anew compound which 
is soluble.* 

The term Solution is applied both to the process 
itself, and the resulting liquid j the fluid being term- 
ed a solvent or menstruum. 

In the process of solution the solid body may be 
considered as under the influence of two antagonist 
forces, viz. the cohesion of its own particles, which 
tends to preserve it in a solid state, and the attraction 
between its particles and those of the fluid which 
tends to bring it into the liquid state. Hence in 
proportion to the relative energies of these opposing 
forces the body will be easy or difficult of solution ; 
and whatever diminishes the cohesion of its particles 
will increase its solubility. 

Exp. 15. — Place a small lump of marble in a wine-glass, and a 
small quantity of the same substance, previously reduced to 

* Where we cannot pronounce decidedly upon the perfect transparency of a 
lijiuid, recourse may be had to the filter — if the solid be merely mechanically 
diffused through the liquid it will remain upon the filter and the liquid will pass 
through perfectly transparent. 



32 ELEMENTS OF CHEMISTRY. 

powder, in another, pour upon each weak sulphuric acid ; the 
powdered marble will dissolve much more rapidly than the solid 
lump. 

Solution is also promoted by agitation which 
removes from the solid the portion of the fluid 
already saturated with it, and brings a fresh portion 
in contact. 

Exp. 16. — Into a wine-glass filled with water tinged blue with 
infusion of cabbage* let fall a lump of solid tartaric acid. The 
acid, if left at rest, will only change to red that portion of the 
infusion which is in immediate contact with it ;— but stir the 
liquor and the whole will become red. 

Solution is promoted by heat, and hot liquids in 
general are more powerful solvents than cold ones. 

Exp. 17. — To 4 fluid ounces of water, at the ordinary tempera- 
ture, add 3 ounces of sulphate of soda {Glauber'^s salt) in powder ; 
a portion only will be dissolved. Apply heat and the whole of 
the salt will disappear. 

To this law, however, there are several exceptions ; for many 
salts are equally, or nearly equally, soluble in cold as in hot water. 

In most cases of solution there is a certain point 
at which the force of affinity between the solid and 
fluid will be balanced by the cohesion of the solid, 
beyond which solution wnll not proceed ; this point 
is called saturation^ and the resulting compound a 
saturated solution, 

Exp. 18. — If successive portions of sugar or salt be added to a 
measured quantity of water, they will gradually disappear or be 
dissolved, but if the addition be continued, a portion of the solid 
will fall to the bottom of the vessel, the liquid having taken up 
as much as it is capable of, or become saturated. 

The only physical quality of the solid which is changed by 
solution is its cohesion. 

This point of saturation in any fluid is very differ- 
ent with respect to different solids ; a fluid may dis- 
solve its own weight of some solids, but of others 
one half, or one fourth, or even but a few hundredth 
parts. 

After a menstruum has been fully saturated with 
one body, it may nevertheless be capable of dissolv- 

*Made by pouring hot water upon purple cabbage leaves, and after some tirae 
passing it through a piece of clean cloth. 



LIXIVIATION. 



33 



ing another ; and when saturated even with a second, 
may still retain the power of dissolving a third 5 but 
rarely in such large quantities as it would do were 
it pure. 

Exp. 19. — Saturate a given portion of water with comraon salt ; 
taking care that a small quantity remains undissolved at the 
bottom of the vessel ; if some nitre be now added, we shall find 
that not only this second body will be dissolved, but that the 
residual salt of the first solution will also disappear on agitation. 

The explanation of this apparent paradox is to be 
found in the simple fact, that new compounds ac- 
quire new powers as solvents. 

Lixiviation is merely solution performed with a 
particular view, to separate a substance which is 
soluble in water from others which are not ; it is 
effected by pouring upon a mixture of various solids 
a sufficient quantity of water and allowing it to per- 
colate through them. The solution is termed a Ley 
or Lixivium.^ 



The vessels usually employed 
by the chemist, in making solu- 
tions are small flasks or matrasses 
{a) ; the common Florence oil 
flask is very convenient for such 
purposes, or larger vessels called 
Bolt heads {b)A 



Although the cohesive attraction is overcome by 
the opposing force of chemical affinity, it still exists 
and is constantly tending to reunite the particles 
which are dissolved, and to restore their aggrega- 
tion ; for no sooner is a portion of a solvent removed 

*This operation is generally performed on a large scale in tubs or vats, having a 
hole near the bottom containing a wooden spigot and faucet. A layer of straw is 
placed at the bottom of the vessel over which the substances are spread and covered 
by a cloth, after which hot or cold water according as the substance is more or les^ 
soluble is poured on. The water is drawn oif and fresh portions successively added 
imtil all that is soluble is removed. 

jThe operations o^ Maceration^ Digestion^ Infusion^ Decoction, &c.are moroly 
processes of solution, 




ELEMENTS OF CHEMISTRY. 



by evaporation, than they become approximated, and 
are again brought within the limits of their mutual 
attraction, when they reunite and the solid reappears. 

The fluid menstruum may be either removed by 
sponta)ieons evaporation, occasioned by the simple 
exposure of a considerable surface to the atmosphere ; 
or by that which is produced by heat.* 

If the solid matter thus recovered from a solution, 
be of a vegetable nature it is termed an Extract and 
the process is termed Inspissation ; whereas saline 
bodies so obtained, assume regular forms denomina- 
ted Crystals and the process in that case is called 
Crystallization, 

Where a solid is to be recovered from a more 
valuable liquid, as alcohol, for instance, the process 
termed Distillation^ is instituted, whereby the 
chemist is enabled to carry on his operation in close 
vessels, so as to collect the fluid that is volatilized, 
and to preserve it without loss. 

For the accomplishment of this object various 
forms of apparatus have been contrived. The com- 
mon Still, as here represented, is the one more 
generally employed for the preparation of spirits, 
distilled waters, &c. 




*Por this purpose basins, or evaporating dishes of porcelain (Wedgewood's 
ware) glass, silver and sometimes platinum are employed. They are flat bottomed, 
shallow vessels, presenting a wide surface to the air. For most purposes evapo- 
rating dishes may be made of the bottoms of broken flasks, retorts, &c. which may 
be cut round by means of a hot iron or ring of wire, or by tying a piece of string 
moistened with spirit of turpentine and then inflaming it. Watch glasses aie some- 
times used. 



DISTILLATION. 35 

This apparatus consists of the following parts. 
The Boiler^ a^ the body of which is partly sunk in 
a furnace, the head or capital, h^ from which passes a 
pipe, whicli enters the spiral tube, or worm, placed 
in a tub of cold water, c, termed the Refrigeratory. 
The still is usually constructed of copper, but the 
worm is of pewter. The body, head, and worm 
require to be luted^ together, in order to prevent 
the escape of any portion of the volatile product. 

* Lutes^ or Cements^ are used either to close the joinings of chemical vessels, to 
prevent the escape of vapours or gases ; or to protect vessels from the action of the 
fire which might otherwise crack, fuse, or calcine tkem. In this latter case the ope- 
ration is termed lorication^ or coating. To prevent the escape of the vapours of 
water, spirit, and liquors not corosive, the simple application of slips of moistened 
bladder will answer well for glass ; and paper with good paste for metal. Bladder 
to be veryMhesive should be soaked sometime in water moderately warm, till it feels 
elamray ; it then sticks verv vveli ; but if it be-smeared with white of Q,gs,.^ instead of 
water, it will adhere still cioser. 

There is a great variety of receipts for the composition of Lutes, all of which are 
referable to one of the three following classes, viz. 

I. Unctuous and Resinous Lvtes. — 1. Melt eight parts of beeswax with one of 
turpentine, and according as it may be required to be more or less consistent or 
pliable, add different proportions of common powdered rosin, and some brick dust. 
This lute adheres very closely to glass, and is not easily penetrated by acrid vapours ; 
it has the advantage also of being very plastic and manageable ; but it cannot 
sustain a heat above 140^. — 2. Melt spermaceti, and while it is hot, throw in bits 
of caoutchouc. This is an excellent lute where much heat is not employed. — 3. A 
solution of shell-lac in alcohol added to a solution of isinglass in proof spirit, 
forms a cement that will resist moisture. — 4. The lute best calculated for confining 
acid vapours for any length of time is termed the Fat Lute, and is made by taking 
any quantity of tobacco-pipe clay, thoroughly dry, but not burnt, powdering it in an 
iron mortar, mixing it gradually with drying linseed oil, and then beating them 
together for a long time to the consistence of a thick paste Much manua^ labour is 
required, and it should be continued until the mass no longer adheres to che pestle. 
The edges of the glass or vessel, to which it is to be applied, should be perfectly dry. 
Good glazier's putty, which is made of chalk, beat up with drying linseed oil, much 
resembles the fat lute in quahty. 

II. Mucilaginous and Gelatinous Lutes. — 1. Linseed meal, kneaded up with 
water to a sufficient consistence, and applied tolerably thick over the joinings of 
the vessels ; or Almond meal, tieated in a simifar way, form very convenient lutes, 
which <lry and become firm in a short time. — 2. Smear shps of linen on both sides 
with white of e^g, tiien apply these neatly to the joinings, and when applied shake 
loosely over them some finely powdered quick-lime. This lute dries speedily, is 
extremely hard and cohesive, impervious to water, and impenetrable by most kinds 
of vapour. 

TIL Earth]} Lutes. — These are intended for operations which require a high 
temperature. — 1. Mix burnt gypsum {Plaster of Paris) in powder, with w-ater to 
the consistence of a thick cream, and apply it immediately. This forms a lute 
which sets as soon as it is applied, and is firm ; but a slight blow will easily crack 
it. 2. A very valuable fire lute may be made of about one part of glass of borax, 
five parts of brick-dust, and five parts of clay finely pow^dered together and mixed 
with a little water when used. 

In every instance, where a lute or coating is applied, it is adviseable to allow it to 
dry before the operation is commenced ; and even the fat lute, by exposure to the 
air during one or two days after its application, is much improved in firmness. The 
clay and sand lute is perfectly useless except it be previously quite dry. In applying 
a lute, the part immediately over the juncture should swell outward, and its diameter 
should be gradually diminished on each side. — For other lutes and the method of 
applying them 8ge J^ewr^f's C>ii;t»«5tr^, Vol. let lire's Dutionar^. 



56 



ELEMENTS OF CHEMISTRY. 



The substances, to be acted upon, having been intro- 
duced into the boiler, and submitted to heat, are 
soon volatilized and raised into the head, whence 
they pass into the ivorm. where they are condensed, 
a«Kl issue in drops from the lower end of the pipe, d. 
By degrees, the water in the refrigeratory becomes 
warm, and requires to be ref)laced bv a fresh por- 
tion ; and thence the necessity of the tub being 
furnished with a stopcock, by which the heated 
water may be drawn oflf, without disturbing the 
apparatus. 

In some cases a ^lass vessel termed an Memhic, 
is used, and is represented by the accompanying 
sketch. It consists of two parts ; the body, a^ for 
containing the materials, 
and the head, 6, by which 
the vapour is condensed, 
and from which it is carri- 
ed by a pipe into a receiv- 
er, c. It will be perceived 
that the head is of a. con- 
ical fi^ure,^and has its ^ 
external circumference or 
base depressed lower than its neck, so that the vapours 
which rise, and are condensed against its sides, run 
down into the circular channel formed by its de- 
pressed part, from whence they are conveyed by 
the nose or beak into the receiving vessel. 

The use of the Alembic is now almost superseded 
by that of the Retort and Receiver, whose con- 
struction and applications we have next to con- 
sider. 

The Retort is a bottle with a long neck, so bent 
as to make with the belly an angle of about sixty 
degrees, The most capacious part of the vessel is 
termed its belly ; its upper part is called an arch or 
roof ; and the bent part, the neck, A retort may 
be either plain or stoppered, as shown in the follow- 




RETORT AND RECEIVER. 



37 



ing figure, in this latter case it is said to be tubu- 
lated. 

To the Retort, a Receiver is a necessary append- 
age ; and this may either be plain as engraved below 
(c) or tubulated. To some a pipe is added, as may 
be seen in the figure representing the apparatus for 
the distillation of Nitric acid. Such a receiver is 
principally useful for enabling us to remove the 
distilled liquid, at difierent periods of the process, 
and is termed a quilled receiver."^ 

In order to facilitate the condensation of the va- 
pour, the neck of the retort is occasionally lengthen- 
ed by an intermediate tube {b) termed an adopter^ 
the wider end of which slips over the retort neck, 
while its narrow extremity is admitted into the 
mouth of the receiver, as here exhibited. 




*For the convenient introduction of the liquor into the retort several instruments 
have been contrived. When it is to be added at distant intervals during the process, 
the best contrivance is the one here exhibited, which consists of a bent tube, a, with 
a funnel at the upper end. When the whole is to be introduced at once, it is either 
done through the tubulure by the common funnel ; or, if into a plain xetort, through 
a funnel of a construction similar to the one here represented ; 





which will enable the operator to pour in the liquor without touching the inside of 
the retort neck, which by being soiled would contaminate the result of tlie process. 

4 



38 



ELEMENTS OF CHEMISTRY. 



Retorts are made of earthenware, and of green, or 
of white glass, according to the operations for which 
they are destined. They are also heated in several 
different modes. When the vessel is of earthen- 
ware, and the substance to be distilled requires a 
strong heat to raise it into vapour, the naked fire is 
applied. Glass retorts are usually placed in heated 
sand ; and, when of a small size, the flame of an 
Argand lamp, cautiously regulated, may be very 
safely used. If the nature of the operation be such 
as to require a glass vessel, and a high temperature, 
the retort must be coated.* 

In many processes, where a large proportion of the 
extricated matter is partly condensable into a liquid 
and partly a gas, which is not condensed without 
the presence of a considerable proportion of water, 
we may make use of what is called Woulfe^s appa- 
ratus.! 

*For this purpose a mixture of moist common clay, or loam with sand, and cut 
shreds of tow or flax, may be em.ploycd. The following is the mode of applying 
it. After kneading the coating material, so as to render it very plastic, let it be 
spread out on a flat table, and lay the bottom of the retort in the middle of the mass; 
then turn up the edges of the cake, so as to bring it round the whole of the vessel, 
pressing it down in every part with the fingers, until it applies uniformly and closely, 
if the distillation be performed by a sand heat, the coating need not be applied 
higher than that part of the retort ^vhich is bedded in sand ; but if the process be 
performed in a furnace the whole body of the retort and that part of the neck also 
which is exposed to the fire, must be carefully coated. 

tit consists of a seri«s of receiving vessels containing water. 




The first receiver (J) has a right angled glass tube, open at both ends, fixed into 
its tubulure ; and the other extremity of the tube is made to terminate beneath the 
surface of distilled water, contained, as high as the horizontal dotted line in the 
three-necked bottle, (c.) From another neck of Ibis bottle, a second pipe proceeds, 
wliich ends, hke the first, under water, contained in a second bottle (a.) To the 
central neck a straight tube, open at both ends is fixed, bo tliat its lower end may be 



CRYSt ALLIZ ATION. 39 

By the process of evaporation then, under which 
subject we have included Distillation, the fluid part 
of a solution may be driven off, and separated from 
the fixed matter with which it was combined. We 
have next to consider under what circumstances, and 
in what forms, the 50//^ constituent may be recovered. 

No sooner is a portion of a menstruum removed 
by evaporation, or by other means to be hereafter 
described, than the particles reunite, and the solid 
reappears. In the accomplishment of this effect, the 
particles of certain bodies, as if actuated by a species 
of polarity, assemble in groups of a determinate 
figure, while others aggregate in confused masses. 

The process, by which the particles of a body 
are enabled to arrange themselves into determinate 
forms, is termed Crystallization ; while the regular 
bodies so produced are called Crystals. 

To impart freedom of motion to the particles of 
a solid body, we must confer upon it either the 
liquid, or aeriform condition ; and it is equally evi- 
dent that, in order to allow such particles to arrange 
themselves with regularity, or to crystallize^ the 
body must be allowed to return to its solid form 
slowly, and without disturbance or interruption. 

Solution and fusion are the means by which the 
body is rendered fluid ; evaporation and slow cool- 

a little beneath tlie surface of the liquid. Of these bottles any number may be em- 
ployed that is thought necessary. Ihe materials being introduced into the retort, 
the arrangement completed, and the joints secured, the distillation is commenced. 
The condensable vapour collects in a liquid form in the balloon 6, while the evolved 
gas passes through the bent tube, beneath the surface of the water in c, which con- 
tinues to absorb it till saturated. When the water of the first bottle can absorb no 
more, the gas passes, uncondensed, through the second right-angled tube, into the 
water of the second bottle, which in its turn becomes saturated. Any gas that may 
be produced, which is not absorbable by water, escapes through the bent tube e, and 
may be collected, if necessary. The use of the perpendicular tubes in the middle 
necks is to prevent the interruption of the process by an accident, which would 
perpetually occur without such a contrivance ; for if in consequence of a diminished 
temperature, an absorption or condensation of gas should take place in the retort, 
and of course in the balloon &, it must necessarily ensue that the v/ater of the 
bottles c aad a, would be forced by the pressure of the atmosphere, into the balloon, 
and possibly into the retort, which might cause a dangerous explosion ; f but, with 
the additions of the central tubes, a sufficient quantity of air would under such 
circumstances, rush through them to supply any accidental vacuum. 

tThis transfer of a liquid from one vessel to another, in consequence of the 
formation of an imperfect vacuum, is termed aUsorptioji-, and is highly annoying to 
tlie inexperienced operator. 



40 ELEMENTS OF CHEMISTRY. 

ing, or a gradual abstraction of the solvent by the 
action of chemical affinity, are those by which it is 
made to crystallize. 

In some cases heat at once overcomes the cohesive 
force, and the substance is converted into vapour, 
which on being slowly condensed will assume a 
regular crystalline form; it is thus that Benzoic acid, 
Camphor, Iodine, &c. may be made to assume the 
form of regular crystals. The process is termed 
Sublimation. 

Exp. 20. — Into a large glass jar, inverted upon a flat brick tile, 
and containing near its top a branch of any plant moistened with 
water, introduce a flat, thick, piece of heated iron, on which 
place some gum benzoin in coarse powder. The benzoic acid, 
will be vaporized and ascend in white fumei?, which will at length 
condense in delicate crystals upon the branch. 

It has been ascertained that every substance, in 
crystallizing has a tendency to assume a particular 
geometric figure ; thus common salt crystallizes in 
cubes ; Epsom salt in four sided prisms, alum in 
octoedrons, &c.* 

Every crystal may be divided by means of proper 
instruments : and if split in certain directions, pre- 
sents smooth and plane surfaces. If split in other 
directions, the fracture is rugged, and is not guided 
by the natural joining of the crystal.! 

A method of developing the structure of crystals, 
by a new process, which appears greatly superior to 
that of mechanical division, has been described by Mr 
Daniell. It consists in exposing any moderately solu- 
ble salt to the slow and regulated action of a solvent.! 

In order to obtain well-formed crystals from saline 
solutions, three essential circumstances are required; 
viz. Time^ Space, and Bepose. By time the super- 
abundant fluid is slowly dissipated, so as to allow 
the particles of the salt to approach each other by 
insensible degrees, and without any sudden shock ; 
in which case they unite according to their constant 

* To those who are desirous of prosecuting the science of crystallography we would 
recommend " A familiar introduction to crystallography," by H. I. Drooke, Esq. 
t See "Manual" p. 8. 



WATER OF CRYSTALLIZATION. 41 

laws, and form a regular crystal ; indeed it is a 
general rule, that the slower the formation of a 
crystal the more perfect will be its form; the larger 
its size, and the harder and more transparent, its 
texture ; while on the contrary, too speedy an 
abstraction of the separating fluid will force the 
particles to come together, suddenly, and, as it were, 
by the first faces that offer ; in which case the crys- 
tallization is irregular, and the figure of the crystal 
indeterminate, and, if the abstraction be altogether 
sudden, the body will ever form a concrete mass 
with scarcely a vestige of crystalline appearance. 
Space, or sufiBcient latitude for motion, is also a 
very necessary condition. A state of repose in the 
fluid is absolutely necessary for obtaining regular 
forms ; all symmetrical arrangement is opposed by 
agitation, and a crop of crystals obtained under such 
circumstances would necessarily be confused and 
irregular.* 

In the act of separating from the water in which 
they were dissolved, the crystals of almost every 
salt carry with them a quantity of water, which is 
essential to the regularity of their form, as well as 
to their transparency and density, and which cannot 
be expelled without reducing them to shapeless 
masses. It is termed their water of crystalliza- 
tion, and its proportion will be found to vary very 
essentially in the diflerent salts ; in some instances 
constituting more than half their weight, as in the 
case of sulphate of soda, carbonate of soda, nitrate 
of ammonia, &c. while in others it is extremely 
small ; and yet, however it may difier in different 
salts, it always bears, in the same salt, the same 
definite ratio to the solid saline matter. This water 
appears to be in a state of combination with the salt, 
and not simply interposed between its laminse, 

*The whole art of crystallizing substances is founded upon these obvious truths, 
although on many occasions, to ensure perfect success a certain address is required 
in the manipulation, which has enabled particular manufacturers to produce articles 
Tery superior to ordinary specimejis. 

4* 



42 ELEMENTS OF CHEMISTRT. 

Where the water of crystallization exists in a large 
proportion, and the solubility of the salt is greatly 
increased by elevation of temperature, the applica- 
tion of heat is often sufficient to liquify the crystals, 
producing what is termed watery fusion. 

The water of crystallization is retained in differ- 
ent salts with very different degrees of force. Some 
crystals lose it by mere exposure to the atmosphere, 
in consequence of which they pass into the state of 
a dry powder, and are said to effloresce ;^ while 
others, on the contrary, not only retain it very 
strongly, but even attract more; and, on exposure 
to the atmosphere, become liquid, or deliquesce. 

The means by which a solution is made to sur- 
render its saline charge in a crystalline form are 
two fold, viz. by Refrigeration and Evapora- 
tion. 

When the salt to be crystallized is considerably 
more soluble in hot water, as sulphate of soda, 
nitrate of potassa, &c. it is only necessar}^ to saturate 
hot water with it, and to set it aside to cool. In 
conducting this process, how^ever, the cooling of the 
fluid ought to be gradual, for the more slowly the 
water cools, the more regular will be the crystals 
obtained, whereas, if a boiling solution be suddenly 
cooled, it will let fall, in a shapeless mass, all the 
excess of salt that was dissolved by the agency of 
heat. It will be expedient, therefore, to place the 
solution, while very hot, on a sand bath, or in a 
warm place, and to lower its temperature by slow 
degrees; the vessel should, at the same time, be 
covered with a cloth to prevent the access of cold 
air. After the solution is perfectly cold, and all the 
excess of crystalline matter is separated, the residual 
liquoV may be treated as directed in the following 
page. 

* This circumstance is very annoying to the collectors of crystals ; such as are 
liable to this change should be preserved in jars containing a portion of water ; or, 
where the salt is not acted upon by oil, the crystals may be etfectually defended by 
raejely smearing their surfaces with that substance. 



CRYSTALLIZATION^ 43 

If we have a saturated solution of a salt which is 
not more soluble in hot than in cold water; it is 
evident that refrigeration will not advance its crys- 
tallization. In such a case we must proceed to 
abstract a portion of the menstruum : and this may 
be accomplished in two ways^ viz. 

A. By Evaporation through the agency of Heat ^ 

In common cases all that will be required is to 
continue the process of evaporation, until a drop of 
the solution when placed upon a cold body shows a 
disposition to crystallize ; or, at farthest, until we 
observe a thin film of saline matter, called a pellicle^ 
creeping over the surface of the liquid , which indi- 
cates that the attraction of the saline particles for 
each other, is becoming superior to their attraction 
for the water; and that the solution, therefore, when 
left undisturbed, will crystallize. After the first 
crop of crystals has been thus made to separate, the 
evaporation may be repeated, and another crop 
obtained, and so on, until by a succession of evapo- 
rations and coolings, the greatest part of the saline 
charge is surrendered in a crystalline state. 

If the crystallizable salt be perfectly pure, the 
whole of its solution may be thus crystallized ; but 
it often happens that, if two or more salts exist in 
the same menstruum, after crystals have been obtain- 
ed by several evaporations and coolings, the remain- 
ing portion of the fluid, although saturated with 
saline matter, will nevertheless refuse to crystallize; 
in which state it is technically denominated mother 
ivater. 

The above process affords a convenient mode of 
separating salts, which coexist in the same solution; 
for on carefully reducing the quantity of the solvent 
by evaporation, the salt w^hose particles haVe the 
greatest cohesion will crystallize first. If both 
salts are more soluble in hot than in cold water, the 
crystals will not appear till tlie liquid cools. But if 



44 ELEMENTS OF CHEMISTRY. 

one of them, like common salt, is equally soluble in 
hot and in cold water, crystals will appear, even 
during the act of evaporation. In this way we may 
separate nitre from common salt, the crystals of the 
latter being formed during evaporation ; while those 
of nitre do not appear till some time after the fluid 
has cooled. 

In some cases, the affinity of a salt for its solvent 
is so great, that it will not separate from it in the 
form of crystals ; but will yet crystallize from 
another fluid, which is capable of dissolving it, and 
for which it has a weaker affinity ; thus, for instance, 
potassa cannot be made to crystallize from its w^atery 
solution, but will yet separate, in a regular form, 
from its solution in alcohol. 

B. By Spontaneous Evaporation. 

For this purpose, we must expose the saline solu- 
tion to the temperature of the atmosphere, in vessels 
having a considerable extent of surface, and slightly 
covered with fine paper, or gauze, which may pre- 
vent any dust from falling into the liquor, without 
opposing the progress of evaporation. For this 
operation, it will be advantageous to select a sepa- 
rate chamber well ventilated, and sufficiently light. 
The solution is thus left exposed to the air, 
till crystals are perceived in it, which sometimes 
will not take place in less than four, five, or six 
weeks, or, with some salts, for even a still longer 
period. This is by far the most successful and cer- 
tain of all the processes for obtaining perfect crystals 
of considerable size, and is that which ought always 
to be preferred where time and circumstances will 
allow the election.* 

* After the operation, however, has continued for some time in progress, the active 
vigilance of the operator becomes necessary ; for when the quantity of salt held in 
solution becomes much diminished, the liquid will begin to act upon the separated 
crystals, and to re-dissolve them. The action is, at first, perceptible on their right 
angles and edges ; they become blunted, and gradually lose their shape altogether. 
Whenever this operation commences, the liquid must be poured off, and a fresh 
portion of the solution substituted, otherwise the crystals will be infallibly 
destroyed. 



CRYSTALLIZATION. 45 

The student may exemplify these facts by the 
following simple and striking experiment. 

Exp. 21 — Introduce a fully saturated solution of common salt* 
into a medicine phial of four ounces, so as to occupy about two- 
thirds of it, and cover its mouth loosely with a piece of filtering 
paper ; then place it upon a shelf exposed to light. In the 
course of a fortnight, a cube of salt will be distinguished at the 
bottom of the phial, which will gradually augment in size, until 
it attains a certain magnitude, when if attentively watched, its 
angles will be observed to become less acute, and the crystal will 
gradually lose its figure. 

Crystallization is accelerated by introducing into 
the solution a nucleus, or solid body upon which the 
process begins ; and manufacturers often avail them- 
selves of this circumstance. Thus we see sugar candy 
crystallized upon strings, verdigris upon sticks, &c. 

By placing a crystal of the same nature in a satu- 
rated solution of a salt, and turning it daily, very 
large and perfect crystals may be obtained. And if 
there be two salts in solution, that one will most 
readily separate, of which the crystal has been 
introduced. 

A strong saline solution, excluded from the air 
will frequently crystallize the instant that air is 
admitted; a circumstance unsatisfactorily referred to 
atmospheric pressure. In other cases agitation pro- 
duces the same effect. 

Exp. 22. — Make a saturated solution of Glauber's salt in boil- 
ing water, in a small matrass^ cork it tight, and allow it to 
remain at rest till perfectly cool, the solution will remain fiuid ; 
but on withdrawing the cork crystallization will generally com- 
mence ; should it not, the introduction of a small piece of the 
same salt will usually effect it. 

The presence of light also influences the process 
of crystallization. Thus if we place a solution of 
nitre in a room which has the light admitted only 
through a small hole in the window shutter, crystals 
will form most abundantly upon the side of the basin 

*As common culinary salt usually contains a portion of muriate of ma^nesin, it 
will be necessary to remove this foreign ingredient, by precipitating it trom Uiia 
solution by carbonate of soda, and then to filter the liquid. 



46 ELEMENTS OP CHEMISTRlT. 

most exposed to the aperture through which the 
light enters, and often the whole mass of crystals 
will turn towards it. 

Many saline solutions form arborescent crystalline 
pellicles, when left to spontaneous evaporation, which 
slowly travel up the sides of the basin, and gradually 
proceed down upon the outside. This has been 
termed Saline vegetation^ and may be prevented by 
smearing the edge of the vessel with sweet oil. 



ELECTIVE AFFINITY. 

Having learnt the nature of the species of attrac- 
tion, by which two bodies of a different nature com- 
bine with each other, so as to lose their individuality, 
and to produce a compound with new characters, 
we may next consider the important truth that the 
attractions exerted by any body towards others^ 
are different in their force with respect to each. 

Exp, 23. — Mix together equal weights of magnesia and of 
quicklime, in fine powder, and add diluted nitric acid. After 
some hours, it will be found that a considerable part of the lime 
has been dissolved, but that the whole of the mao:nesia has 
remained untouched. Hence it is clear that nitric acid has a 
stronger attraction for lime, than for magnesia. 

In such a case the nitric acid has been metaphori- 
cally represented as making an election, whence 
this species of Affinity is denominated Elective 
Affinity. 

Upon the discovery of this important law, it 
occurred to Geoffrey, a French chemist, that tables 
might be constructed, which should exhibit the rela- 
tive forces of attraction of any body towards others. 
The substance, whose affinities are to be thus ex- 
pressed, is merely placed at the head of a column, 
separated from the rest by a horizontal line. Be- 
neath this line are arranged the different substances 
for which it has any attraction, in an order cor- 



ELECTIVE AFFINITY. 47 

responding with that of their respective forces of 
affinity ; the substance which it attracts most power- 
fully being placed nearest to it, and that for which 
it has the least affinity, at the bottom of the column. 
The following series, exhibiting the affinities of 
Muriatic acid for the alkalies, and alkaline earths, 
may serve as an example, 

MURIATIC ACID. 



Baryta. 

Potassa. 

Soda. 

Lime. 

Ammonia. 

Magnesia. 

In consequence of the same body uniting with 
others, with different degrees of force, we are 
enabled to decompose a compound by adding any 
substance which has an attraction to one of them 
superior to that by which they were held united, 
Tiie two bodies, between which there is the strongest 
attraction, combine, and the third is separated. This 
may be easily demonstrated. 

Exp. 24. — Heat together, in a flask, nitric acid, and magnesia ; 
these substances will combine, and a nitrate of magnesia result; 
at the same time, make a solution of lime in water, by agitating 
some powdered qaick-lime in distilled water. Let the solution 
of lime be poured into that of magnesia, when a white powder 
will separate, and gradually fall to the bottom of the vessel. 
This powder is found to be magnesia, which is thus disunited 
from nitric acid, in consequence of the strong attraction of lime 
for that acid. 

The following series of experiments, which the 
student may easily perform, affords a farther illustra- 
tion of this law of elective affinity. 

Exp. 25. — Dissolve pure silver in nitric acid, or make a solu- 
tion of nitrate of silver (lunar caustic) in disfilled water. To 
this add mercury, which will be dissolved, and the silver disen- 
gaged. The supernatant fluid will tb«n be a solution of mercury 
in nitric acid. 



48 ELEMENTS OF CHEMISTRY. 

Exp. 26. — To the above solution of mercury in nitric acid, 
present a piece of sheet lead ; the latter metal will be dissolved, 
and the mercury become disengaged. The fluid will then be a 
solution of lead in nitric acid. 

Exp. 27. — If in this solution of lead, a thin piece of copper be 
suspended, the copper will be dissolved, and the lead become 
disengaged. The fluid now is a solution of copper in nitric acid. 

Exp. 28.— In this solution of copper, let a thin sheet of iron 
be immersed ; in a short time the iron will disappear, and be 
replaced by metallic copper, and we have now a solution of iron 
in nitric acid. 

Exp. 29. — Let a strip of zinc be next presented to the solu- 
tion ; the iron will be thus separated, and the sine remain in 
solution. 

Exp, 30. — To the zinc solution, we may now add ammonia, 
■which will instantly combine with the nitric acid, and the zinc 
be thus separated ; the solution will in this case alone contain 
nitrate of ammonia. 

Exp. 31. — Into this solution of nitrate of ammonia pour some 
lime-water, the ammonia will be instantly disengaged (manifest- 
ing itself by a pungent odour) and the solution will be nitrate of 
lime, 

Exp. 32. — If to this solution we add oxalic acid, the lime will 
be precipitated, and what now remains will be merely nitric acid. 

When a body is liberated from a compound by the 
agency of elective affinity, it may either pass off in 
the state of gas, as in experiment 31, or remain in 
solution, or be separated as an insoluble body ; in 
which latter case it is said to be precipitated : the 
substance employed to produce the decomposition 
is termed the precipitant^ while the fluid which 
remains after the operation is called the super- 
natant liquor. 

In those cases where the developed constituent 
assumes an elastic form, it must be obtained through 
the medium of a distilling apparatus connected with 
Woulfe's bottles, as already explained, (p. 38) or by- 
means of a hydro-pneumatic trough^ as will be 
hereafter described. 

As Precipitation is an operation of the highest 
importance, both in a chemical and pharmaceutical 
point of view, it will be necessary in this place to 
enter into some details, in explanation of its nature 



PKECiriTATION. 49 

and uses. It is employed to separate solids from the 
solutions in which they are contained ; to produce 
new combinations, which cannot be readily formed 
by the direct union of their constituents ; to purify 
solutions from precipitable impurities; and to reduce 
a body to a finer state of division than the most 
laboured mechanical process can effect. They are, 
moreover, in this attenuated condition, more easily 
disposed to enter into new combinations; thus, for 
instance, Silica, although reduced to the finest pow- 
der by levigation, may be boiled for some time 
in liquid potassa without being rendered sensibly 
soluble; but, when first precipitated from a state of 
chemical solution, it is not only readily soluble in 
that menstruum, but it is even capable of being acted 
upon b}^ certain acids. 

In some cases the precipitate is separated by the 
precipitant, in consequence of the latter having a 
greater affinity for the liquid, and thence weakening 
its attraction to the substance which is held in solu- 
tion, as occurs when water is added to spirit of 
camphor, or, alcohol to the solutions of certain salts. 
In other cases, the precipitate is an insoluble com- 
pound formed by the union of the added substance 
with that which was previously held in solution, as 
takes place upon the addition of sulphuric acid to a 
solution of baryta. (See p. 54, Exp. 33.) 

The vessels usually employ- 
ed for precipitation are tall jars, 
which are sometimes narrower 
at the bottom than at the 
mouth, so as to allow the pre- 
cipitate to collect by subsi- 
dence, and the supernatant liquor to be afterwards 
decanted off. 

When the chief object of the process is to obtain 
the precipitate in a pure form, it is necessary to wash 
it, after it is separated by filtration, and to dry it by 
ai heat not exceeding 212° ; for the accomplishment 

WITHDRAWN 




y 



so 



ELEMENTS OF CHEMISTRY. 



of which an extremely useful apparatus is represent- 
ed in the figure below.* 

The changes which occur, through the agency of 
that species of elective attraction which we have just 
considered^ have been ingeniously represented by 
diagrams. The following scheme illustrative of the 
decomposition of Spirit of Camphor, by water, may 
serve as an example. 

Spirit and Water. 



Spirit 

of 

Camphor 



Rectified Spirit 



Water. 



Camphor 



Camphor. 



The original compound (Spirit of Camphor) is 
placed on the outside, and to the left of the vertical 
bracket ; the included space contains the original 
principles of the compound (Rectified Spirit and 

''A exhibits the vessel, with its 
diflercnt parts in situ. 

B, shows the same apparatus 
supported by the riug of a staud 
over an arg[and lamp; its parts 
being detached in order to render 
the description of them more 
perspicuous. The vessel a is of 
sheet iron, or copper, japanned 
and hard soldered ; c is'a conical 
vessel of very thin glass, having 
7 a rim, which prevents it, when in 
^ its place, from entirely slipping 
into a; and rf is a moveable ring, 
wiiicli keeps the vessel c in its 
place. When the apparatus is 
in use, water is poured into a, 
and the vessel c, containing the 
substance to be dried, is immers- 
ed in the water, and secured by 
the ring d; the whole apparatus 
is then suspended over an argand 
lamp. The steam escapes by 
means of the chimney i, through 
which a little hot water, may be 
occasionally poured, to supply 
the waste by evaporation. Where our object is to ascertam with accuracy the 
weight of any precipitate, as in thn case of an analysis, if we previously estimate 
the weight of tl>e filler employed, we may at once arrive at the conclusion witJjout 
incutring t!io trouble artd falhcy of »fp,i»ating the matter deposited upon it. 




COMPLEX AFFINITY. 51 

Camphor,) and also the body (water) which is added 
to produce decomposition. Above and below the 
horizontal lines are placed the new results of their 
action. The point of the lower horizontal line 
being turned downwards denotes that the Camphor 
falls down, or \s precipitated ; while the upper line 
being perfectly straight, shows that the new com- 
pound (water and spirit) remains in solution. Had 
both the bodies remained in solution, they would 
both have been placed above the upper line. Had 
both been precipitated, they would have been placed 
beneath the lower one. Had either one or both 
escaped in a volatile form, such a result would have 
been expressed b}'- placing the volatilized body above 
the diagram, and turning up the middle of the upper 
line ; thus if we add sulphuric acid to carbonate of 
lime, a sulphate of lime is precipitated, and the 
carbonic acid escapes in a gaseous form, and is repre- 
sented as follows. 

Carbonic acid gas. 



Carbonate 

of 

Lime 



Carbonic acid 

Sulphuric acid 
Lime 



V 

Sulphate of Lime. 



Double Elective Mtractionj or Complex Af- 
finity^ takes place when two bodies, each consisting 
of two principles are presented to each other, and 
mutually exchange a principle of each ; by which 
means two new bodies, or compounds, are produced, 
of a different nature from the original compounds. 
In this case it frequently happens, that the com- 
pound of two principles cannot be destroyed, either 
by a third or fourth separately applied ; whereas, if 
this third and fourth be combined, and placed in 
contact with the former compound, a decomposition, 



52 



ELEMENTS OF CHEMISTRY. 



or a change of principles, will ensue. For instance, 
if to a solution of sulphate of soda we add lime- 
water, no decomposition takes place, because the 
attraction of the sulphuric acid is stronger for the 
soda than for the lime ; so again if muriatic acid be 
added to the same salt no change is induced, since 
the sulphuric acid attracts soda more powerfully than 
tlie muriatic acid. But if the lime and muriatic acid 
previously combined (muriate of lime) be mixed 
with the sulphate of soda, a double decomposition 
is effected. The lime, quitting the muriatic acid, 
unites with the sulphuric; and the soda being sepa- 
rated from the sulphuric acid, combines with thQ 
ijiuriatic. These decompositions, like those pro- 
duced by single affinity^ may be expressed by dia- 
grams. 

Muriate of Soda, 



Sulphate 

of 

Soda 



Soda 



Muriatic acid 



Sulphuric acid 



■Lime 



Muriate 

of 
Lime. 



Sulphate of Lime, 

On the outside of the vertical brackets are placed 
the original compounds (Sulphate of soda, and Muri- 
ate of lime) above and below the horizontal lines, 
the new compounds produced {Muriate of Soda^ 
and Sulphate of Lime,) the upper line being straight 
indicates that the muriate of lime remains in solu- 
tion, the dip of the lower line that the sulphate of 
lime is precipitated. 

There exist numerous extraneous circumstances 

*" which are constantly operating in modifying and 

even reversing the laws of chemical affinity. These 

circumstances are. Quantity of matter ; — Coke- 



INSOLUBILITY. 53 

sion ; — Tnsohtbility ; — Specific Gravity ; — Elas- 
ticity ; — Efflorescence ; — Temperature ; — and Me- 
cha7iical pressure. It will be necessary to examine 
each of these powers in succession, in order to 
establish some conclusions with respect to their 
force and value. 

1. Quantity of matter. Although many of the 
cases which have been adduced in support of the 
fact, that excess in quantity of matter will com.- 
pensate for deficiency of affinity^ may undoubtedly 
admit of a different explanation, still it cannot be 
denied, that chemical decompositions are frequentU^ 
influenced by the ponderable quantities of the sub- 
stances placed within the sphere of action ; whence 
manufacturers operating on a large scale will fre- 
quently obtain results which never arise in the pro- 
gress of a scientific experiment. 

2. Cohesion, The influence of this force has 
been already considered (p. 31.) and we shall here- 
after have occasion to adduce farther evidence of its 
importance. 

3. Insolubility. If there be two bodies, one of 
which is soluble, and the other insoluble, but each 
possessing a nearly equal afiinity to a third ; upon 
bringing such substances into the sphere of attrac- 
tion, the soluble body will possess great advantages 
over its antagonist, for its cohesion, trifling even at 
the outset, must be reduced to almost nothing by 
solution, while that of the insoluble body will 
remain the same. The whole of the soluble body 
will, moreover, exert its afiinity at once, w^iereas a 
part only of the insoluble body can oppose its force. 
Hence it is evident that the former may attach to 
itself the greatest proportion of the third body, 
although it should possess even a weaker affinity 
than the latter, to the subject of combination. In 
some cases, however, insolubility may turn tlie 
balance in favor of the afiinity of one body, when 
opposed to that of another 5 thus, if to the soluble 



B4 ELEMENTS OF ©HEMISTRY. 

compound, sulphate of soda, we add baryta, the new 
compound (sulphate of baryta) being precipitated 
the instant it is formed, and, thus removed from the 
sphere of action, will escape from the dominion 
which the soda might otherwise exert over it, ia 
consequence of its greater quantity, or mass. 

4. Great Specific Gravity, This will necessa- 
rily concur with insolubility, in impeding combina- 
tion in the one case, and in aiding the operation of 
affinity, in the other, as explained in the preceding 
section. 

5. Elasticity^ or Volatility^ will operate by 
separating the particles of bodies so widely, as to 
remove them out of the sphere of their mutual 
attraction. 

6. Effloresence^ like Precipitation, tends to re- 
move one of the bodies from the operation of affinity. 

7. Temperature, This is by far the most im- 
portant of all the extraneous forces which are capa- 
ble of modifying chemical affinity; in fact, the other 
forces fall more or less under its dominion ; that 
cohesion is thus diminished has been shown under 
the history of Solution (p. 31 ;) and it is equally obvi- 
ous that the solubility, specific gravity, and elasticity 
of bodies will be affected by the same power. The 
following experiment will show how far tempera- 
ture, by favouring volatility, may modify, or even 
reverse the order of chemical affinity. 

Exp. 33 — To a solution of nitrate of potassa add alcohol, the 
spirit will immediately unite with the water, and the salt be 
precipitated, if the temperature be now raised, tfie alcohol will 
rise on account of its volatility, and the nitre be re"di.<-solv- 
ed ;— or, 

Exp. 34. — Into a solution of carbonate of ammonia, pour one 
ef rauriate of lime ; a double decomposition instantly takes place, 
carbonate of lime fails down, and muriate of an»raonia floats 
above. Let this liquid mixture be now boiled for some time ; 
exhalation of ammoniacal g^as will be perceived, and the carbonate 
of lime will be re-dissolved, as may be shown by the farther 
addition of caihonate of ammonia, which will cause an earthy 
precipitate from the liquid which, prior to ebullition, was merely 
muriate of amcionia. 



TESTS, OR REAGENTS. 55 

8. Mechanical Pi^essxire^ The effects of this 
force are chiefly manifested in producing the combi- 
nation of aeriform bodies, either with each other, or 
with liquids or solids. 

There remains to be noticed a case of attraction, 
which has been termed Disposiiig Affinity ; in 
which two bodies incapable of combining, are made 
to unite chemically by the addition of a third sub- 
stance, although it may have no apparent affinity for 
either. Thus water is a compound of oxygen and 
hydrogen* iron has an attraction for oxygen ; but 
so little superior to that of hydrogen for the same 
body, that it is unable to decompose water, at a low 
temperature, or, at least, with any energy; but, if a 
small quantity of sulphuric acid be added, the decom- 
position instantly proceeds with very considerable 
rapidity. The Sulphuric acid is said to exert a 
Disposing affinity. 

TESTS, OR REAGENTS. 

From what has been already stated upon the sub- 
ject of chemical affinity, it will follow that the appli- 
cation of certain bodies to different solutions will, by 
producing changes which are striking to the senses, 
detect the presence of very minute proportions of 
particular ingredients. Such bodies are termed 
TestSy or Reagents,^ To illustrate their agency, 

^^--^K * The inost convenient bottle for containing a 

^^.^^-'"''^ i \ chemical test is a common ounce phial, through 

^^'"''"^ V^\ the cork of which should be introduced a piece 

x^ -"^ of glass tube of small bore, two or three inches* 

tj ^^^.^"""'^ lt>ng, and bent at one end to an obtuse angle, as 

•^^^ ^^j,^-"'*'''^ here represented. On inverting the phial, and 

Z^^^^''*^''^"""''^ grasping the bottom part of it, the warmth of the 

^ hand expels a few drops whicli may be directed 

Oupon any minute object. When the flow ceases, it 
may be easily renewed by setting down the bottle 
_-^ for a moment, with its mouth upv.ards (whidi 

^ admits a fresh supply of cool air,) and then proceeding as before. In 
y\ [v some cases where extremely minute quantities are required, as in the 
1 1 ) application of concentrated alkalies or acids, a bottle with an elongated 
stopper, as exhibited in tiie annexed sketch, wiil be found very con- 
venient for enabling the operator to take up a single drop, and to allow 
it to fall upon any body under examination. 
The liquid to be examined is frequently introduced into glasses or tubes, bat as 
this arrangement necessarily requires a certain quantity of materials, a slip of glass 



54 ELEMENTS OF CHEMISTRT* 

let US take a portion of spring water, whose purity 
it is an object to ascertain ; if we introduce a few 
drops of a solution of the Nitimte of Silver^ and a 
white precipitate follows, we may conclude from 
the phenomena that the water in question contains a 
muriatic salt or some carbonated alkali or earth ; 
such an effect, however, from these latter bodies, 
may be at once prevented by the previous addition 
of some nitric acid. To show the extreme delicacy 
of nitrate of silver, as a test for any muriatic salt, 
it may be stated, that if two glasses be filled with 
distilled water, and the finger is merely dipped into 
one of them, the silver test will actually indicate the 
impurity thus introduced. If the water should con- 
tain any sulphuric salt, the Nitrate of Baryta will 
indicate its presence by a white precipitate, which 
will not disappear on the addition of nitric acid, as 
it would, were the precipitate a carbonate. The 
presence or absence of lime may be inferred from 
the effect occasioned in the water by Oxalate of Am- 
monia, which will precipitate this earth, although it 
should exist in extremely minute quantities. These 
few examples are sufficient for present illustration, 
others will occur in our progress. 

On the Proportions in which Bodies combine: 
and on the Atomic Theory* 

In the chemical combination of bodies with each 
other we remark. 

1st. Some bodies unite in all proportions ; for 
example, water and sulphuric acid, or water and 
alcohol. 

2dly. Other bodies combine in all proportions, as 
far as a certain point, beyond which, combination 

may be very conveniently substituted, or on some occasions, a piece of common 
■writing paper. Where our object, hov/ever, is to collect the precipitate for the 
purpose of ascertaining its weight, or of submitting it to other processes, we are 
necessarily compelled to work on a larger scale. For merely determining the com- 
position of a liquid, without any reference to the proportions of its ingredients, the 
slip of glass will answer every intention ; and it is quite surprising to what a degree 
of accuracy an experienced eye will arrive in deducing a conclusion from the colour, 
density, and other appearances of the precipitate thus produced. 



ATOMIC THEORY. 57 

no longer takes place. Thus water will take up 
successive portions of common salt, until at length 
it becomes incapable of dissolving any more. In 
cases of this sort, as well as in those included under 
the first head, combination is weak and easily de- 
stroyed, and the qualities which belonged to the 
components in their separate state continue to be 
apparent in the compound. 

3dly. There are many examples in which bodies 
unite in one proportion only. In cases of this sort 
the combination is generally energetic ; and the 
characteristic qualities of the components are no 
longer observable in the compound. 

4thly. Other bodies unite in several proportions j 
but these proportions are definite, and on the inter- 
mediate ones, no combination ensues. When a body 
combines with another in several different propor- 
tions, the numbers indicating the great proportions 
are exact simple multiples of that denoting the 
smallest proportion. 

On facts of this kind is founded what is termed 
the Atomic Theory of the chemical constitution 
of bodies * 

If but one combination of any two bodies is found 
to exist, the elements of the compound are supposed 
to be united atom to atom singly. But if several 
compounds can be obtained from the same elements, 
they are supposed to combine in proportions express- 
ed by some simple multiple of the number of atoms. 

Chemists have found it convenient to refer the 
atomic w^eight of bodies to some standard or unit 
which is assumed as the weight of an atom of some 
well known substance. Some have assumed Hy- 
drogen for this purpose because it is the lightest 
body and unites with others in the smallest propor- 
tion ; others have assumed oxygen from its almost 
universal relations to chemical matter. 

* See "Manual;" page iT. 



5$ ELEMENTS OP CHEMISTRY. 

What some chemists call an atom others call a 
ptoportiouj and to express the system of definite 
ratios in which bodies reciprocally combine, referred 
to a common standard, reckoned unity, the terms 
Chemical Equivalent are employed. 

Thus if 100 parts of sulphuric acid and 68 of 
muriatic acid neutralize 118 of potassa, and the same 
quantity of sulphuric acid neutralizes 71 of lime, 
we may infer that 68 of muriatic acid will also 
neutralize 71 of lime. In such a case 100 parts of 
sulphuric acid and 6S of muriatic are said to be 
Equivalents of each other.* 

The proof, which establishes the nature of chemi- 
cal compounds, is of two kinds, synthesis and analy- 
sis, (p 27.) 

When the analysis of any substance has been carri- 
ed as far as possible, we arrive at its most simple 
principles, or elements ; by which expression w^e 
are to understand, not a body that is incapable of 
further decomposition, but only one which has not 
yet been decomposed. 



HEAT, OR CALORIC. 

When a person places his hand on a piece of hot 
metal, a particular sensation is excited ; or if he 
thrust 'the end of a poker into a fire it soon becomes 
red hot. This is supposed to be owing to something 
passing from the metal to the hand, or from the fire 
to the poker, which, in general language, is called 
Heat, This term, is, however, employed in a 
double acceptation, — ^to denote both the cause of the 
sensation and the sensation itself A more correct 
language is now adopted by chemists, though even 



OAiORIG. 5& 

to it they do not adhere strictly. The word Calorie 
(derived from the Latin calor^ signifying heat) is 
used to denote the cause, while the term Heat is 
still retained to express the sensation excited. By 
Heat then we are to understand the sensation pro- 
duced by a warm body, by caloric the active cause 
of this sensation. Caloric is the most active agent 
in nature. All bodies contain it ; but different 
bodies have different quantities ; and on this depends 
their temperature. It has a tendency to pass from 
one substance to another, though this takes place 
differently, according to circumstances. In some 
cases it passes slowly from particle to particle \ 
in others it darts through the air with immense 
velocity, from one body to another. In either of 
these ways heat is communicated, till an equality of 
temperature is established, unless prevented by the 
operation of some foreign power. 

Besides these, Caloric produces other effects; thus, 
by receiving it a body is enlarged, and, as it con- 
tinues to receive it, the enlargement continues, till 
it becomes either a fluid or vapour. ^ 

Cold is generally believed to be merely the loss 
of caloric ; the particular sensation excited, by what 
is called cold, being occasioned, not by any particu- 
lar agent, but solely by the abstraction of heat. 
In treating of caloric w-e may consider 

1st. Its effects. 

2d. Its communication. 

Sd. Its sources. 

EFFECTS OF CALORIC. 

The general effects of caloric are four. — Expan- 
sion^ Liquefaction^ Evaporation^ and Incandes- 
cence, 

EXPANSION. 

The most obvious and familiar effect of caloric 
tipon bodies is Expansion. When bodies are heat- 



60 



ELEMENTS OF CHEMISTRY. 



ed they are increased in bulk and as they eool they 
return to their former dimensions; hence caloric is 
inferred to separate their particles and is regarded 
as the repulsive power which is constantly opposed 
to the force of attraction. 

The expansion of solids may be made apparent 
by heating a rod of iron, of such a length as to be 
included, when cold, between two points, and the 
diameter of which is such, as barely to allow it to 
drop through an iron ring. When heated, it will 
be found incapable of passing through the ring. 

This property of metals has been applied to the 
construction of an instrument for measuring tempera- 
ture, called 1^ pyrometer. 

An instrument of this kind is here represented. 




Upon a flat piece of mahogany are fixed brass 
studs g g^ on which the metallic bar ff is placed. 
One end of this bar bears against a lever 6 at a 
point very near its fulcrum ; the other end of this 
lever, which is bent, bears against another lever c, 
the lower extremity of which is an index. Beneath 
this index is a graduated arc d. When we wish 
to immerse the bar in hot water, or to apply heat 
gradually through the medium of water, the bar 
is passed through the brass box «, which has an 
aperture at each end. An opening is left in the 
board immediately under the box, to allow the ap- 
plication of a lamp. The small expansion of the 



/ 

EXPANSION. 61 

metallic bar is magnified by the first lever in the 
proportion of the distances of the point of pressure 
from its plane, and from its other extremity ; and 
this magnified efiect is again magnified by the other 
lever, so that an expansion of the 400th part of an 
inch corresponds to a whole inch on the scale. {See 
Ferguson^ s Led.) 

The degree of expansion is not the same for all 
solids, and even differs materially in substances of 
the same class. Thus, the metals expand in the 
following order, the most expansible being placed 
first; zinc, lead, tin, copper, bismuth, iron, steel, 
antimony, palladium, platinum. 

Solids are less expansible than liquids, and gases 
or aeriform bodies more than liquids. 

The expansion of liquids may be shown by the 
following experiment. 



Into a glass vessel, (a) having a narrow 
neck, introduce some spirits of wine, and 
apply the heat of a lamp ; or immerse the 
ball of the vessel in hot water — the spirits 
of wine will expand ^nd rise in the narrow 
neck. 



Liquids differ also in their relative expansibilities: 
ether is more expansible than spirit of wane, and 
spirit more than water, and water more than mercu- 
ry. Those liquids are generally most expansible 
w^hich boil at the lowest temperaturo. 

Exp. 35. — This may be rendered evident by partially filling 
several glass tubes of equal diameters, furnished with bulb«, with 
the different liquids and placing them in hot water, as the Hquids 
expand, they will rise to different heights in the tubes. To 
render this more apparent the liquids may be tinged with some 
colouring matter. 
6 




62 ELEMENTS OF CHEMISTRY.' 

Exp. 36. — The expansion of air may be shown by filling the 
body of the vessel (ap. 61i) with water and, keeping the finger over 
the orifice of the neck, inverting it in a vessel of water, the air 
will rise and occupy the body of the vessel ; apply the heat of a 
lamp, and the air will expand and cause the water to descend 
in the neck of the vessel. 

If a bladder filled with air, the neck of which is 
closely tied, be held before a fire, it will become 
fully distended and may even be burst by continu- 
ing and increasing the heat. 

The expansion of liquids is not equable for equal 
additions of heat at different temperatures. It might 
be expected that the enlargement would proceed 
regularly with the increase of temperature, but this 
is by no means the case ; it proceeds in a greater 
ratio. The nearer a fluid is to its freezing point, 
the less is the expansion, as is remarkably the case 
with water. Of course, as it approaches its boiling 
point, the enlargement becomes greater ; hence it is 
most nearly equal at the middle between these. 
Quicksilver, therefore, which has a great range of 
temperature between that at which it freezes, and 
that at which it boils, is, at the heats to which it is 
usually subjected, more uniform in its expansion 
than any other fluid, and hence it is preferred for 
thermometers. 

As heat increases the bulk of all bodies, it is obvi- 
ous that change of temperature is constantly produc- 
ing changes in their density or specific gravity, as 
may be easily demonstrated. 

Exp. 37. — If we apply heat to the bottom of a fiask containing 
water and small pieces of amber, that portion of the fluid, which 
is nearest to the source of heat, is expanded, and becoming 
specifically lighter, ascends, and is replaced by a colder portion 
from above. This, in its turn, becomes heated and dilated, and 
gives way to a second colder portion ; and thus the process goes 
on, as long as the fluid is capable of imbibing heat. 

In air, similar currents are continually produced, 
and the vibratory motion observed over slated roofs 



EXPANSION. 



63 



which have been heated by the sun, depends upon 
this circumstance; the warm air rises and is replaced 
by that which is cooler. 



n 



W] 



Exp. 38. — Put into a jar of water a glass ball, 
or any object, so as just to float at a, and plunge 
this into a vessel with a warm fluid ; as the caloric 
enters from the one into the other the ball will 
gradually fall to the bottom, 6, shovving that the 
density of the water has been diminished. On the 
contrary if a ball be put into Avater, so as just to 
sink to the bottom, 6, and the vessel be surrounded 
by a cold mixture, as the fluid loses its heat tlie 
ball will rise to a, shewing that the density cr speci- 
y fie gravity, has become greciter. 



The general law of expansion is applied to many 
useful purposes, but it is also a source of great in- 
convenience. The cracking of glass vessels, and 
other bodies of a similar nature, is occasioned by it. 
When warm water is poured into a cold tumbler, 
the particles within, as they receive heat, expand : 
but owing to the slow transmission of it through the 
glass, the particles on the outside coiitinue for soiric 
time as they were ; they do not therefore yield to 
those within, and a crack is the consequence. On 
the contrary when cold water is put into a warm 
glass, the inner particles, as they loose their heat, 
contract, while the outer ones remain expanded 5 
they do not follow the others, and hence also the 
vessel is cracked. This points out the necessity of 
warming or cooling glass gradually, to allow time 
for the uniform exj)ansion or contraction of the 
particles. The cracking is also prevented by hav- 
ing the vessel very thin, by which, should they be 
suddenly heated or cooled, the w^hole is almost 
instantaneously expanded or contracted.* 

* There is, perhaps, no artist put to so much inconvenience from expansion as a 
clock-maker. Clocks which are made of metal, are much aliecied by a ciiange in 
:the volume occasioned by an alteration of temperature, which causes the movements 
to vary at diiferent times ; but the pendulums are more particularly affected. The 
(jiiickness of the vibrations of ^ pendulum depends on its len^tli — the longer it is, the 



64 



ELEMENTS OP CHEMISTRY. 



Though expansion is a source of great inconve- 
nience yet it is put to many useful purposes. A 
Vv'heelwright daily resorts to it, for fixing the hoops 
on the wooden part of the wheel. For this purpose, 
having made it a very little less in diameter than 
the other, he expands it by bringing it to a red heat, 
and when in this state, he puts it on the wheel, and 
instantly dashes cold water on it, by which it con- 
tracts, and embraces the wheel tightly. It fre- 
quently happens that the stopper of a bottle becomes 
fixed ; it may however, in general, be taken out, by 
having recourse to expansion. The corner of a 
towel is dipped in warm water, and applied around 
the neck, so as to throw caloric into it, and cause it 
1o expand, by which its diameter is enlarged before 
the stopper receives any heat, so that, by giving it a 
slight blow with a piece of wood, it is easily re- 
iiioved. 

Before finishing the subject of expansion, we have 
to notice the exceptions to this law. When pure 
clay, or any substance containing it in considerable 
quantity, is exposed to heat, it contracts instead of 
expanding. As in this case, the clay does not regain 
its original bulk when it cools, it is not to be con- 



fewer the vibrations in a given time. Tf, therefore, it be lengthened 
by heat, they become fewer, and consequently the movements of 
the clock are slower. Luckily, however, a remedy for this defect has 
been discovered, and in the very source of the inconvenience itself. 
All the different kinds of Compensation Pendulums are on the same 
L.rinciple, but the simplest, and the one most easily understood, is 
That called the Gridiron Pendulum, so termed from its appearance, 
ft is composed of two metals, iron and brass, the latter of which 
< xpands twice as much as the former, by the same addition of heat. 
When properly constructed it consists of two iron rods a, 6, and 
four brass rods c, d, fixed in the cross bars c, /, ^, h. The upper end 
of a is tiie point of suspension ; and after passing through a hole in 
f , /, its lower one is fixed to the bar g, h. The lower extremity of 
h has the ball attached to it ; wliile, after passing through a hole in 
o"^ A, its upper one is fixed to e,/. The brass rods are all riveted to 
the cross bars. Suppose heat is applied to this pendulum, by 
which each iron rod expands half an inch, the ball would thus be 
thrown an inch down ; but as the brass expands twice as much as 
the iron, each rod would be lengthened an inch, and throw it an 
inch up, the four rods acting merely as one. Since then, the 
lengthening of the brass raises it just as much as that of the iron 
tends to depress it, the pendulum is kept always of the same length, 
and the movements of the clock are not liable to be affected by 
a change of temperature^ 




Expansion. 65 

sidered a real exception ; for were it so, it ought 
to contract by heat, and expand by cold. Many 
bodies in passing from fluid to solid, enlarge, even 
though they are parting with caloric, as is remarka- 
bly the case with water, ice occupying more space 
than the fluid from which it is formed. That water 
expands while freezing, is proved by ice always 
floai^hg, shewing that it is lighter, bulk for bulk than 
water. 

The force exerted by the enlargement of water, 
while freezing is astonishing, vessels, though made , 
of metal, being easily burst by it : hence the cause 
of the frequent bursting of pipes during winter, the 
water, when freezing, expanding with such force as 
to tear asunder the lead of the pipe. This points 
out the necessity of laying them, a considerable way 
under ground, to prevent the frost from reaching 
them. Experiments have been made to ascertain 
the actual force of the expansion. In one of these a 
brass globe having a cavity of an inch in diameter, 
was burst, by filling it with water, plugging up the 
rnouth, and freezing the fluid. To accomplish this, 
it was calculated that the force exerted must have 
been equal to about 27,720 pounds. 

The exceptions mentioned are not to be consider- 
ed real, the substances having undergone a change; 
the clay has lost moisture, or some other matter, and 
the water has passed from fluid to solid. There is 
one real deviation, however, in the case of water at a 
certain temperature. When we apply heat to water 
at 32^^ instead of expanding, according to the gen- 
eral law, it contracts, and it continues to do so till it 
reaches about the 40th degree, after vvhich, still con- 
tinuing the heat, it begins to enlarge. On the con- 
trary, when we apply cold to water at 40 ; instead 
of contracting, it actually expands, and continues to 
do so until it is frozen. 

The change in volume is not great, but it may be 
shewn by the following experiment. 
6* 



60 



-iO 



66 ELEMENTS OF CHEMISTRY. 

Exp. 39.— -Provide a small tube with a bulb at one 
fcud, pour into it water at the temperature of 50*^ and 
Wiark its height. Plunge the bulb into ice, as the 
heat is withdrawn the liquid falls in the stem till it 
comes to 40^. After this, instead of continuing to 
sink, it begins to rise ; and when at 32" it is higher in 
the tube than at 40^ it must therefore have expand- ^-^ 
cd. Now heat the bulb, the water, instead of rising 
will fall in the tube, s^o that at 40*^ it will be lower 
than when at 32*^ ; it must therefore have contracted. 

From this it is evident that water at 40*^, is of 
greater density, that is, bulk for bulk, it weighs more, 
or is of greater specific gravitj, than at 32^. 

The important results of this remarkable deviation 
from the general law will be explained when treating 
of Fluidity. 

By far the most useful application of expansion is 
making it a measurer of temperature^ or of the 
state of a body in relation to its power of exciting 
the sensation of heat, and of occasioning expansion. 
Our senses enable us to estimate the temperature of 
bodies but very imperfectly, for when we touch a 
warm or cold body we compare the sensation with 
that we have just beforeexperienced. If we place 
one hand in snow and immediately immerse it in 
water, the latter will feel warm ; but if we warm the 
other hand before a fire and then immerse it in the 
water it will feel cold. A substance then will feel 
warm at one time and cold at another, though its 
temperature in both cases be the same. We thus 
see the necessity of having some fixed standard 
of comparison ; as expansion is an effect of caloric 
of much regularity and extent it has been resorted 
to for this purpose. When two bodies produce the 
same increase or diminution of volume in a third 
body to which they are equally applied, we say that 
they are at the same temperature, and any body is 
at a higher or lower temperature as it produces a 
greater or less expansion in another body with 
which it is in contact. To convey therefore any 
precise notion of temperature we are obliged to de- 
scribe the degree of expansion produced in some 



THEKMOMETER. 67 

one body which has been taken by general consent 
as a standard of comparison. The standard most 
commonly employed is a quantity of quicksilver 
contained in a glass ball which terminates in a long 
tube. This instrument is called a Thermometer from 
the Greek words therme^ heat^ and metroii a 
measure. 

To Sanctorio of Padua we are originally indebt- 
ed for the invention. The instrument, however, 
employed by that philosopher was of a very simple 
description, and measured variations of temperature 
by the variable expansion of a confined portion of 
air. This instrument is represented in the margin. 
It consists of a glass tube, eighteen inches long, 
open at one end, and blown into a ball at the 
other. If a warm hand be applied to the ball, 
the included air will expand, and a portion be 
expelled through the open end of the tube. 
And if, in this state the aperture is quickly 
immersed in a cup filled with some coloured 
liquid, it will ascend in the tube, as the air in 
the ball contracts by cooling ; and its altitude 
S vvill in every case depend upon the degree of 
expansion which the air has previously undergone. 
In this manner it is prepared for use, and will indi- 
cate increase of temperature by the descent of its 
fluid, and vice versa. These effects may be exhibit- 
ed, alternately, by applying the hand to the ball, 
and then blowing on it with a pair of bellows. The 
amount of the expansion or contraction is measured 
by a graduated scale attached to the stem of the 
instrument. 

The advantages of the ^^ir Thermometer consist 
in the great amount of the expansion of air, when 
compared with that of any liquid : b}^ which it is 
enabled to detect minute changes of temperature, 
which the mercurial thermometer would scarcely 
discover ; for air is increased in volume by a given 
elevation of temperature, about twenty limes more 



es 



ELEMENTS OP CHEMISTRT. 



than quicksilver. The advantages, however, which 
attend this excessive delicacy are counterbalanced 
by several serious objections. It will be readily 
seen, for instance, that the air thermometer will not 
only be affected by changes of temperature, but by 
variations of atmospheric pressure. 

Professor Leslie, under the name of the Differen- 
tial Thermometer has introduced a very important 
modification of the air thermometer. It consists of 
two glass tubes of unequal length, each terminat- 
ing in a hollow ball, as represented in the annexed 
figure, which are united by a bent tube containing 
coloured sulphuric acid. Whenever a hot body ap- 
proaches one of the bulbs, it must neces- 
sarily drive the fluid towards the other. J) 
It is evident then that this instrument 1 [^ 
cannot be employed to measure variations 
in the temperature of the surrounding 
atmosphere, because, as long as both balls 
are of the same temperature, whatever 
this may be, the air contained in both 
Vv^ill have the same elasticity, and con- 
sequently, the intercluded coloured liquor, 
being pressed equally in opposite direc- 
tions, must remain stationary. If, how- 
ever, any change of temperature is effected 
in one of the balls, the instrument will 
immediately indicate this difference with 
the greatest nicety. The amount of this 
effect is ascertained by a graduated scale, 
the interval between freezing and boil- 
ing being distinguished into 100 equal 
degrees. This thermometer is peculiarly 
adapted to ascertain the difierence of the 
temper it u res of two conli2:uouj§ spots in 
atmosphere, and its application has 
siderable liii;bt upon several of the 
phenomena of caloric. 




same 
thrown con- 
more obscure 



THERMOMETER. 69 

The thermometer in ordinary use consists of an 
hermetically sealed glass tube, terminating at one 
extremity with a bulb. The bulb and part of the 
tube are filled with an appropriate liquid, which, 
when designed to measure very low temperatures, 
is spirit of wine, under other circumstances quick- 
silver is better adapted for the purpose. A graduat- 
ed scale is attached to the stem ; and, whenever the 
instrument is applied to bodies of the same tempera- 
ture, the mercury, or spirit, being similarly expand- 
ed, indicates the same degree of heat. In dividing 
the scale, the two fixed points usually resorted to are 
the freezing and boiling of water, which always take 
place at the same temperature, when under the same 
atmospheric pressure ; the intermediate part of the 
scale is divided into any convenient number of 
degrees. In this country we use the scale of Fahren- 
heit, of which the 0° is placed at 32°, below the 
freezing of water, which is therefore marked 32°, 
and the boiling point 212°, the intermediate space 
being divided into 180 degrees. The scale more 
commonly used on the continent of Europe is that 
of Reaumur, in which the freezing point is 0°, the 
boiling point 80°.* 



r?i 



As the chemist will frequently have occasion 
to employ the thermometer for ascertaining the 
temperature of corrosive liquids, the graduated 
scale should be provided with a hinge, so as to 
double back, and leave the bulb exposed, as 
b represented in the margin. 



O 



For measuring high temperatures, it is evident 
that the thermometer cannot be employed. An 



* See Majnual, page 26. 



70 ELEMENTS OP CHEMISTRY. 

instrument, called a Pyrometer^ from the Greek 
words puT^ fi^^y and metron^ a measure^ has been 
constructed, founded on the property which metals 
possess of expanding by heat. (See Manual page 
22.) 

Different methods have been recommended for 
ascertaining the highest or lowest temperature that 
may occur during any particular period, as during 
night, when there is no one present to observe it. 
The simplest contrivance of this kind is the follow- 
ing. It consists of two thermometers, a spirit of 
wine and a mercurial one, the former for ascertain- 
ing the lowest, the latter the highest heat. Into 
the tube of the former is placed a small piece of 
white enamel, which as the fluid contracts, is brought 




along with it, but on its again expanding does not take 
it with it; it leaves it at the place to which it had 
carried it, and thus the lowest temperature that had 
happened is pointed out. Into the tube of the latter 
is placed a small piece of a needle, so as just to rest 
on the mercury. As the fluid expands, it pushes the 
needle before it and on again contracting, it leaves 
it at that part to which it had carried it, so that in 
this way the highest temperature is ascertained. 
These thermometers are fixed on a board, with the 
balls at opposite sides, the mercurial one horizon- 
tally, the spirit of wine one with the ball inclined 
downwards, so that, when we wish to set them, by 
raising the side next the spirit ball, the enamel and 
needle will come to the surfaces of the fluids. 

It must not be supposed that a thermometer is an 
exact measure of the number of degrees of heat in 



FLUIDITY, 71 

a body ; it points out only the relative number , 
that is, the temperature of one compared with that 
of another. Thus a substance at 50°, is not sup- 
posed to have only 50 degrees of heat. It means, 
that it has 50 more than one at zero. Again, a body 
at 100 is not supposed to be twice as warm, or to 
contain twice as much heat, as another at 50; it has 
only twice as many degrees, reckoning from the 
commencement of the scale. If we knew the point 
at which there is absolute cold, in other words, 
where there is not any heat, and could begin the 
scale there, then the thermometer would indicate 
accurately the caloric — but of this we know nothing. 
We must consider this instrument then as pointing 
out only the difference between the temperature of 
bodies. 

FLUIDITr. 

It has been already proved, that as w^e apply heat 
to a body, it enlarges. In continuing its application, 
the enlargement also continues, till it arrives at a 
certain temperature, when a change of a different 
nature ensues. It now becomes liquid, in which 
ease it is, said to be melted^ liquefied, or fused^ and 
the change is called fusion, or liquefaction^ which 
is the second general effect of caloric. On the con- 
trary, when we apply cold to a fluid, it contracts, 
and continues to do so, till at a certain temperature 
it becomes solid, and it is then said to be frozen or 
congealed. In this way, almost every solid may be 
made fluid, and almost every fluid solid. Hence, as 
liquids at a natural temperature contain heat, and as, 
by abstracting it, we can make them congeal, we 
infer that the solid is the natural form of these 
bodies. Those solids that cannot be fused by heat, 
as coal, are such as are decomposed before they 
arrive at their melting point ; hence, if means be 
adopted to prevent the decomposition, they can be 
easily melted. 



72 



ELEMENTS OF CHEMISTRY. 



The change from solid to fluid occurs at a certain 
temperature in each ; thus, ice melts at 32, sulphur 
at 21S ; every other substance has its point of lique- 
faction fixed. When, however, a body has arrived 
at this temperature, the whole of it does not sud- 
denly become fluid ; the melting on the contrary, 
goes on gradually. This is owing to an absorption 
of caloric ; for the important fact has been satisfac- 
torily established, that when a solid is changed to 
fluid, it absorbs a large quantity of heat, and which 
does not, in the smallest degree, raise its tempera- 
ture. It has been said, therefore, to become latent, 
or concealed, and is therefore called latent heat, to 
distinguish it from that causing the temperature, 
and which is called free caloric. That a large 
quantity of heat enters a body during liquefaction 
is easily proved. 













F 


L 




<d. 


L 


A 






B 


'60 
50 


^4 


\32 




J 


p2 
> 



Exp. 40.— Put into a jar, A, some ice, 
and into another, B, some ice-cold water, 
and in each let there be a thermometer. 
By adding to these equal quantities of 
caloric, the results will be very different. 
To get equal quantities of caloric, we have 
only to take equal measures of a substance 
at the same temperature as boiling water, 
which is always, under certain circumstan- 
ces, at the same heat. If a measure of 
boiling water be added to the water in the jar B, the temperature 
is affected, as is shewn by the rise of the fluid in the thermometer, 
say to 40. On adding the same measure to the ice A, part of 
the latter is melted, but there is not the slightest rise of tempera- 
ture, the thermometer still continues at 32. The addition of 
another measure to the water, causes a greater elevation, say of 
50, but, on adding it to the ice, more of it is melted, but the 
thermometer still stands at 32. In this instance, then, the heat 
has been absorbed b^ the ice, but the temperature is not elevat- 
ed ; indeed, it is necessary to continue the addition, till the 
whole of it is melted. If, after this, we gtill throw it in, the 
temperature begins to be affected. Here, then, caloric is absorb- 
ed, but without raising the temperature ; it is therefore said to 
become latent. 

The reverse of this may be expected, — that when 
a substance passes from fluid to solid, it should give 



LATENT HEAT. 73 

forth heat, without having its temperature lowered ; 
and that this really occurs, has been proved satisfac- 
torily with water. 

Exp. 41. — If two vessels, one with ice-cold spirit of wine, 
another with ice-cold water, and each having a thermometer in 
it, be placed in a freezing mixture of salt and snow, caloric will 
be taken from both ; by which the latter will be frozen, but the 
former will continue fluid. The thermometer in the spirit will 
sink, say to ; but that in the water will still remain at 32. 
Here, then, we have been withdrawing heat from spirit, so as to 
bring it down to ; we must also have been taking it from the 
water, yet its temperature is not diminished. Whence, then, has 
come the caloric that must have been taken away? The water 
being brought down to its freezing point, begins to congeal ; and, 
during its congelation, must give forth heat. 

Here, then, it is proved, that a substance, in pass- 
ing from fluid to solid, gives out a large quantity of 
caloric, but the loss of which-floes not in the least 
diminish its temperature; in other words, its latent 
heat is disengaged. 

When a solution of Glauber's salt, is made sud- 
denly to crystallize, its temperature is considerably 
augmented ; and when water is poured upon quick- 
lime a great degree of heat is produced by the solidi- 
fication which it suffers in consequence of chemical 
combination ; congelation is, therefore, to surround- 
ing bodies a heating process and liquefaction a cool- 
ing process. 

By this absorption of caloric, during the passage 
of a body from solid to fluid, and by its extrication 
w^hen it is changed from fluid to solid, m.my curious 
and important occurrences of nature, and many of 
the operations of chemistry, may be accounted for. 
When heat is applied to any substance, tallow, for 
instance, it is very slowly melted ^ and though we 
continue the heat for a considerable time, there may 
some of it still remain solid. This is accounted for 
by the absorption of caloric, a large quantity of which 
mast be added, before the whole of the solid can be 
melted. Hence also the cause of the time required 
to melt immense masses of ice, or collections of 
7 



/4 ELEMENTS OF CHEMISTRY. 

snow. It is not merely necessary that the state of 
the weather be such, as to raise their temperature 
to the melting point ; a great deal of caloric must 
be thrown in, otherwise they will not be melted. 
Were it not for this, dreadful deluges would follow 
the liquefaction of ice ; but as the heat is slowly 
absorbed, the ice and snow are gradually melted, and 
the water formed is thus distributed over the surface 
of the globe. The reverse of this is equally benefi- 
cial ; for did this law not exist, the moment that the 
water of a lake is cooled to its freezing point, the 
whole of it would suddenly congeal, and prove 
destructive to the life of its inhabitants. Whereas, 
owing to the necessary extrication of caloric, the 
freezing goes on slowly ; besides, heat is thus given 
out, which, in no small degree, lessens the intensity 
of the cold that would otherwise ensue. 

By this absorption of heat, we are also enabled to 
account for the production of cold, by what are called 
freezing mixtures. Thus, when a solid and a fluid, 
or two solids, are mixed, and they act on each other, 
by which they become fluid, heat must be absorbed, 
to enable them to put on this form ; they therefore 
take it from any body brought into contact with 
them. Ice and salt, when mixed, become fluid, and 
produce cold, both of them, during their liquefaction, 
absorbing heat ; if therefore, heat is not added, they 
must take it from themselves; that part of the free 
caloric becomes latent, by which the temperature is 
reduced. 

Exp. 42. — Dilute a portion of nitric acid with an equal weight 
of water; and, vv^hen the mixture has cooled add to it a quantity 
of light fresh fallen snow. On immersing the thermometer in 
the mixture, a very considerable reduction of temperature will 
be observed. 

Exp. 43. — Mix quickly together equal weights of fresh fallen 
snow at 32*^ and of common salt, cooled, by exposure to a freezing 
atmosphere, down to 32**. The two solids, on admixture will 
rapidly liquefy, and the thermometer will sink 32** or to 0**. If 
a small quantity of water contained in a thin glass tube be placed 
in the mixture it will be frozen. 



EVAPORATION. 75 



EVAPORATION. 



By applying heat to a fluid, it expands, and con- 
tinues doing so till it arrive at a certain temperature. 
Here it undergoes another change. The cohesion 
among its particles is so far overcome, that it passes 
into the state of vapour ; and the process is called 
Evaporation^ which is the third general effect of 
Caloric. The conversion of a fluid into vapour is 
well illustrated, in the familiar instance of boiling 
water, which, when heated to a certain point, is 
converted into vapour, or steam. The agitation, 
called boiling, is owing to the vapour generated 
below, rising through the water above it. If the 
heat be continued long enough, the whole of the 
fluid is evaporated. 

When we withdraw heat from vapours, they are 
condensed, or again become fluid. It is well known, 
that if a cold object, as a plate of metal, be held 
near the mouth of a tea-kettle in which water is 
boiling, it is instantly covered with moisture, owing 
to the condensation of steam. That a vapour is con- 
densed as its temperature falls, may be proved in 
another way, and still more satisfactorily ; but, 
before stating the experiment, it must be premised, 
that the air of the atmosphere, though a light fluid, 
yet, from its great bulk, presses on the surface of 
the earth, and of course on all other objects, with a 
weight of 15 lb. on the square inch \ and which 
pressure is equal to that of a column of mercury of 
30 inches, or of water of about 2^2 feet. 

Exp. 44. — To prove that vapour is condensed as its 
temperature falls, put a little water into a flask, A, and 
boil it for some time, by which the whole of the air is 
expelled, and that part not occupied bj the fluid is 
filled with steam. When in this state, cork it tightlj, 
and cool it, then plunge the mouth of it into a basin of 
water, B, and remove the cork, and the moment that 
this is done, the fluid will rush up, so as to fill it, being 
forced in by the pressure of the air on the surface of 
the liquid, C, proving that there must have been a 
vacuum, or emptv space, from the condensation of 
the steam. 




76 



ELEMENTS OP CHEMISTRY. 



The part of the thermometric scale at which 
bodies assume the form of vapour varies in almost 
every substance. Some evaporate at a low tempera- 
ture, while others require the most intense heat we 
can excite; indeed, there are some which have not 
been procured in vapour, the heat we are able to 
apply not being sufficient to evaporate them. 

Though bodies pass off in vapour at different 
temperatures, )^et under the same circumstances, the 
vaporific point of a fluid is always the same. Thus, 
water boils at 212, mercury at 656. There is one 
circumstance, however, that materially affects the 
boiling point, which is the pressure. As it is 
increased, it becomes higher, but when diminished, 
it is lowered. That the boiling point is lowered as 
the pressure is diminished, may be proved in differ- 
ent ways. By means of an air-pump, we are enabled 
to withdraw the air from a bell-glass, or receiver, 
so that any substance placed under it must have less 
pressure than when exposed to the atmosphere.* 

*It is necessary here to ex- 
plain how the air-pump acts. 
This will be most easily un- 
derstood by attending to the 
figure, which represents a ver- 
tical section of a pump, in its 
simplest form. A is the bell- 
glass, or receiver, that is to be 
emptied of its air, placed on 
the plate of the pump, B C. 
This communicates by means 
of a tube D, with the syringe 
E, in which there is the piston 
IT, that moves upwards and 
downwards, but quite air-tight. 
At G, the opening of the pipe n 
n, there is a valve which ** ' 
allows air to flow from the 
receiver into the syringe, but 
prevents its return. In the 
piston there is a tube with a 
valve at H, which allows air 
to pass from the under to the 
upper part of the syringe, but 
prevents it from going down 
again. The construction of 
this valve is very simple ; it is merely a small piece of oiled silk, tied loosely over 
the mouth of the tube. When the air passes through, it resists it ; but on again 
attempting to return, it forces it down on the tube, which thus prevents it from 
passing. When we wish, then, to exhaust the receiver A, by raising the piston F, 
the air, owiag to its elasticity, expands, and is thus divided between it and the 
syringe, the valve in the piston being shut when it was raised, by the pressure of 




1> 




SBtTLLITION. 77 

If a substance be placed in the receiver, and the 
air be withdrawn, it must sustain less pressure than 
when exposed to the atmosphere. To prove, then, 
that the boiling point of a fluid is lowered as the 
pressure is diminished, if a jar with a mixture of 
equal measures of cold and boiling water be placed 
under the receiver, and the air withdrawn, it begins 
to boil, and will continue to do so for some time, 
even though the temperature be perhaps 100 degrees 
below the usual boiling point. 

That the boiling point of a fluid is lowered as the 
pressure is diminished, is proved also in another 
way. If water be boiled in a flask for some time, 
the whole of the air of the vessel is expelled, and 
the upper part of it is filled with steam. If, in this 
state, it be closed tightly, and plung- 
ed instantly into cold water, it boils 
briskly, and continues to do so for 
some time ; but if it be plunged into 
boiling water, the ebullition ceases. 
On again putting it into the cold water, 
it begins to boil, and on again placing 
it in the warm fluid, it ceases to do so. 
In this instance, when the vessel is 
closed, and put into the coM fluid, the 
vapour in the upper part is condens- 
ed ; there is thus produced a vacuum ; and as the 
fluid within is relieved of its pressure, it boils, even 
though it is below its boiling point. On putting it 
into warm water; the vapour is prevented from being 
condensed ; it exerts, therefore, a pressure on the 
fluid nearly the same as that of air; and as the 

the air above it, which is thus kept from passing through it into the lower part of 
the cylinder. On again forcing the piston down, the valve at G is shut, while that 
at li is opened ; the air the-efore below, being prevented from returning into the 
receiver, escapes at H. W^hen the piston is raised, tlie valve at H is shut, and that 
at G is opened, the air in the receiver is therefore again divided between it and the 
syringe, and on again forcing the piston down, the air dravrn from the receiver is 
expelled at H. In this way, by alternately raising and depressing the piston, the 
greater part of the air may be removed- It is evident, however, that we cannot 
take out the whole ; for when the elasticity of that left becomes very sligiit, it 
ceases to move the valve, so that any farther working of the pump does not draw 
out more. 




78 ELEMENTS OP CHEMISTRY. 

temperature is below the point of ebullition, it does 
not boil. Here, then, by keeping the flask in cold 
water, the fluid, by the condensation of the vapour, 
is kept under a diminished pressure, by which the 
boiling point is lowered. In this way it may be 
reduced many degrees; indeed, did no pressure 
exist on fluids, there would not be any body in 
that state; it would instantly assume the form of 
vapour. 

Exp. 45 — Into a long glass tube closed at one end, introduce 
a small quantity of ether ; fill up the tube with quicksilver, until 
the ether reaches the open extremity, close this with the thumb, 
and invert it in a cup, on removing the thumb a portion of the 
quicksilver will fall into the cup, leaving a space in the upper 
part of the tube. By grasping: the tube with the hand, where the 
ether floats on the surface of the column of quicksilver, sufficient 
heat will be communicated to cau't the ether to boil and pass 
to thestate of vapour, which, as it fills the upper part of the tube, 
will press upon the qu;cksilver and depress it. In this experi- 
ment the pressure of the atmosphere is counterbalanced by the 
column of mercury, and the ether boils in the vacuum above, as 
will be more fully explained when treating of the barometer. 

If instead of diminishing, we increase the pres- 
sure, the boiling point becomes higher. Thus, if 
heat be applied to water in a close vessel, it may be 
raised many degrees beyond 212 without boiling, the 
vapour at first formed exerting an additional pressure 
on the fluid, and thus preventing its ebullition. The 
apparatus by which this is most easily shewn, is 
that called P a phi' s digester . It is a strong metallic 
vessel with a lid, secured to it by luting. In the 
lid there is a stop-cock, and there is also another 
opening, shut by a stopper, loaded with a certain 
weight, to prevent the too great accumulation of 
steam ; for when it is collected in gre^^t quantity, 
the weight is raised, and the superfluous vapour 
allowed to escape. When water is heated in this 
apparatus, it may be raised maij} degrees beyond 
the boiling point; but after removing it from the 
firO; the moment the stop- cock is opened, so as to 



BOILING POINT. 79 

relieve it of its additional pressure given by the 
steam, it begins to boil, and continues to do so for 
some time, shewing that its temperature must have 
been far beyond its usual boiling point, the caloric 
that kept up the ebullition, being that which had 
raised the fluid above this. It has been ascertained 
by experiment, that water may in this way be 
brought up to 400, or even 500 ; indeed, were the 
vessel of sufficient strength, it might be made much 
higher. 

As the pressure which fluids sustain from the air 
is greater at one time than another, the boiling point 
varies. In this country, the range of the barometer, 
the instrument used for ascertaining the pressure of 
the atmosphere, is about 3 inches, from 28 to 31, 
and it has been ascertained, that for each inch of 
diflference the boiling point of water is altered 1^ 
degree of the thermometer ; it may therefore vary 
nearly 5^. It has been already mentioned, that in 
the construction of a thermometer, (See page 69.) 
one of the fixed points of the scale is found by 
plunging it into boiling water. It w^as, however, 
stated, that there was one circumstance to be attend- 
ed to, the pressure of the atmosphere. In graduat- 
ing thermometers, therefore, we must attend to the 
height of the barometer. We must either seize the 
opportunity when it is at its average height, 29.8, 
at which water boils, at 212°, or we must make 
allowance for the difierence, IJ degree for each 
inch it is above or below it. That is, if the barome- 
ter should be at 30.8, we must mark the height of 
the fluid in the thermometer, when plunged in boil- 
ing w^ater, as 21 3J ; if it should be at 28.8, it must 
be 210J, at which temperatures water boils, when 
the barometer is at these heights. 

It has been already proved, that a solid, when be- 
coming fluid, absorbs caloric, without having its 
temperature elevated 5 the same occurs when a fluid 
is changed to vapour. When water for instance, ar- 



80 



ELEMENTS OP CHEMISTRY. 




rives at its boiling point, the whole of it does not in 
an instant become steam ; on the contrary, the eva- 
poration goes on slowly. That fluids during evapo- 
ration absorb caloric, is proved by a very simple 
experiment. 

Exp. 46. — Put some water into a flask 
A, in which there is a thermometer filled 
with oil or mercury ; place this over a lamp, 
the thermometer gradually rises till the 
fluid begins to boil. If the height of the 
instrument be marked, it will be found 
not to vary in the slighest degree. Sup- 
pose it stand at 212. After leaving it 
there for some time, draw it into the up- 
per part of the flask, so as to have it 
surrounded by the steam B, the tempera' 
ture will be found to continue the same, at [ 
212. Here then caloric was at first flow- 
ing in, in a certain ratio, by which the wa- 
ter was brought to the boiling point, It 
must have continued to flow in afterwards 
in the same ratio, yet the temperature of 
the water, or of the steam, was not aflect- 
ed ; it must therefore be absorbed. 

It may be expected, that as there is an absorption 
of heat during evaporation, there should be an evolu- 
tion of it when vapour is condensed ; and this is 
actually the case, as has been proved satisfactorily, 
with respect to water. By the addition of equal 
weights of boiling water and steam to any body, the 
temperature is very differently affected, that which 
receives the steam becoming the highest. 

Exp. 47. — Take two graduated 
vessels, A and B, and put into 
each 6 ounces of cold water. 
Place the apparatus of the form C, 
with water, over a lamp, and when 
boiling, put the mouth of it into the 
jar A. As the vapour comes into 
contact with the cold fluid, it is in- 
stantly condensed, and converted 
into water; so that by measuring: 
the water formed, we know the 
quantity of steam added. Suppose 
that we continue the experiment 




EVAPORATION. 81 

till the fluid rises to the mark 8, we have added 2 ounces of 
steam ; we have then to pour in boiling water into the other jar, 
to the same height. If a thermometer be now put into them, it 
will be found that the temperature of that which has received 
the steam is much higher than the other. Here then, we have 
added equal weights of water and of steam; both at the same 
heat, (anH that they are so, the last experiment shews), yet that 
which received the steam has its temperature highest ; it must, 
therefore, have acquired most caloric. The steam, then, during 
its condensation, must have given forth heat ; in fact, it gives out 
that which it had previously absorbed during its formation. 

On this principle it can be explained why the 
hand can bear with impunity air at 212, but is in- 
stantly scorched by steam, the steam being condens- 
ed by it, and giving forth a large supply of heat. 

To produce the evaporation of liquids, ebullition 
is by no means essential ; all bodies that boil at mod- 
erate temperatures seem to evaporate, so as to pro- 
duce a certain quantity of elastic matter, in the 
common state of the atmosphere ; and this quantity, 
as well as the degree of its elasticity, is greater in 
proportion as the temperature is higher. 

The general law of the absorption of heat during 
evaporation, and of its evolution when vapours are 
condensed, serves important purposes. When the 
earth is heated by the sun^s rays, the evaporation 
from its surface, and from collections of water, is 
considerable. A large quantity of caloric is thus 
absorbed, and the heat, which would otherwise en- 
sue, is prevented. When, on the contrary, the at- 
mosphere is cooled, the vapour is again deposited ; 
hence the beneficial effects which vegetation derives 
from the deposition of dew, v>rhich is merely the 
condensed moisture of the atmosphere, the heat giv- 
en out by it during its condensation promoting the 
growth of plants. Did this law not exist, we never 
could attempt to boil water ; for the moment it is 
heated to its boiling point, the whole of it would 
pass off in vapour, and cause the vessel to burst with 
prodigious force ; whereas, owing to the necessary 
absorption of heat, this change goes on slowly, the 
vapour escaping as it is formed. 



S0 ELEMENTS OF CHEMISTRY. 

The uses to which evaporation is applied are nu- 
merous and important. Many of the operations of 
chemistry depend on the tendency which bodies have 
to pass off in vapour at diflferent temperatures. Thus, 
when a solid is dissolved in a fluid, they can be sep- 
arated by applying heat ; the latter will be evapo- 
rated, the former will remain in the vessel. When 
this process is carried on without wishing to preserve 
the fluid, it is called evaporation ; but when it is to 
be kept, it is termed distillation. The former is 
practised in open, the latter in closed vessels. Thus, 
when the matter in solution is to be procured, the 
fluid is heated in a shallow basin, so that as great a 
surface as possible may be exposed, by which it is 
quickly evaporated. (See p. 34, J 

The only fluid, the vapour of which we can put to 
any particular use, is water. Steam, owing to the 
large quantity of vapour which it gives forth during 
its condensation, is employed for heating apartments. 
For this purpose, pipes connected with a boiler are 
carried through the room, being, till they enter the 
apartment, either left resplendent, or covered with 
cloth, to prevent the heat from being too quickly 
carried off, and by which the steam would be con- 
densed. Steam is also employed for carrying on dif- 
ferent chemical processes in which too great heat 
would be injurious, as in assisting fermentation, and 
in drying substances gradually, and without the risk 
of burning. When it is used for the last of these, 
suppose for drying gunpowder, the powder is placed 
on boxes, which are filled with it, the condensed va- 
pour being carried off by tubes. When it is employ- 
ed for heating fluids, it is either condensed in them, 
or made to pass throuhg them in worms. Thus, in 
heating water for baths, or in the operations of dyers, 
where water is used for dissolving the dye, a tube 
terminates in each bath, or dye vat, near the bottom, 
where it is condensed ; it gives out its latent heat, 
and warms the whole of the fluid, as was the case 
in experiment 47 mentioned at page 80. In those 



STEAM. 



83 



cases, on the contrary, in which the condensed steam 
would prove injurious to the fluid, in the distillation 
of spirits, for instance, a worm passes through it, 
and comes out at the bottom, (as in the refrigerato- 
ry, page 34.) and being kept constantly full of steam, 
which is condensed by the fluid, the latent heat is 
evolved, and brings up the temperature sufficient 
to carry on the distillation. The condensed steam 
escapes at the mouth of the pipe. In the same way 
brewers heat their fluids for extracting the soluble 
matter from malt. 

It must be kept in mind, that in heating by steam, 
the temperature cannot go beyond 212, the boiling 
point of water, because, w^hen the substance is 
brought up to this, it ceases to condense the steam, 
so that any additional quantity thrown in, though it 
keeps the temperature at this, cannot carry it higher. 
The perfect transparency of steam, and also two 
other important properties, on w^hich depends its 
use as a moving power, viz. its elasticity and its con- 
densibility by a reduced temperature, are beautifully 
shown in a little apparatus contrived by Dr. Wollas- 
ton. It consists of a glass tube 
about 6 inches long and | inch 
bore, as cylindrical as possible, 
and blown out a little at the 
lower end. It has a wooden 
handle, to which is attached a 
brass clip embracing the tube ; 
and within is a piston, which, 
as well as its rod, is perforated, 
as shown by the dotted lines. 
This canal may be occasionally 
opened or closed by a screw at 
the top : and the piston rod is 
kept in the axis of the cylinder 
by being passed through a piece 
of cork fixed at the top of the 
tube. When the instrument is 
used, a little water is put into 




84 ELEMENTS OP CHEMISTRY. 

the bottom ; the piston is then introduced with its 
aperture left open ; and the water is heated over a 
spirit lamp. The common air is thus expelled from 
the tube, and when this may be supposed to be 
effected, the aperture in the rod is closed by the 
screw. On applying heat, steam is produced, which 
drives the piston upwards. On immersing the bulb 
in water, or allowing it to cool spontaneously, a va- 
cuum is produced in the tube, and the piston is forced 
downwards by the weight of the atmosphere. 
These appearances may be alternately produced by 
repeatedly heating and cooling the water in the ball 
of the instrument. In the original steam engine the 
vapour was condensed in the cylinder, as it is in the 
glass tube ; but in the engine as improved by Mr 
Watt, the steam is pumped into a separate vessel, and 
there condensed; by which the loss of heat, occasion- 
ed by cooling the cylinder every time, is avoided. 

INCANDESCENCE, OR IGNITION. 

The three general effects of caloric already treat- 
ed of, may be considered as different degrees of the 
same law, — that it has a tendency to make the par- 
ticles recede, the separation increasing according to 
its addition. The fourth effect is quite distinct. By 
Incandescence^ or Ignition^ is meant, that substan- 
ces, when heated to a certain temperature, become 
red hot, or they emit light as well as heat. 

Incandescence is not accompanied with any chemi- 
cal acrion, and must therefore be distinguished from 
combustion, which is the result not only of the addi- 
tion of caloric, but of an action taking place between 
the air and the body, which when it has ceased, no 
longer remains combustible. Ignition, on the con- 
trary, is altogether independent of the air, and is 
continued as long as the temperature is kept up, and 
may be renewed at pleasure. 

The point of the thermometer at which bodies 
tecome incandescent is differently stated by authors, 



INCANDESCENCE OR IGNITION. B5 

yet it seems to be the same in all ; of course it must 
vary according to circumstances, particularly with 
respect to light, an object which is red hot in the 
dark not being so in day light. Sir Isaac Newton 
fixed the point of incandescence in the dark at 635; 
but this is too low, for mercury boils at 656, and is 
not incandescent. Other experimenters have placed 
it at about 790, while Wedgewood has made it about 
950. It is now generally supposed that ignition in 
the dark occurs at about 800. As the heat is in- 
creased, the emission of light also becomes greater, 
and the colour changes first into red wdth a mixture 
of yellow, and lastly into bright w^hite, beyond which 
there is no change. The degrees at which these 
occur have not been ascertained with accuracy. 
Newton has placed the full red heat at about 750, 
and incandescence visible in daylight at 1000, while 
Wedgewood has fixed it at 1077. The former it has 
been already said, has made ignition in the dark too 
low; we cannot, therefore, place much confidence in 
the results of the experiments on this subject. 

Incandescence occurs only in solids and fluids ; 
that airs do not become so, has been proved by pass- 
ing air through a red hot tube, into a globular ves- 
sel, from which it was allowed to issue by an open- 
ing at the top. On looking into the globe, the air 
was observed not to be incandescent, while a piece 
of metal suspended in it very soon became so. 
Bodies may be made red hot by friction and percus- 
sion, as well as by the direct application of heat. 
Thus, if two hard substances, as flint and steel, be 
struck together, small sparks fly ofi"; or if a piece of 
hard metal be rubbed against a stone, as in the fa- 
miliar instance of a grinding stone, it becomes red 
hot. This is, of course, to be ascribed to the heat 
excited by the friction and percussion being sufficient 
to elevate their temperature to that of ignition, as it 
is well known that heat is evolved during these pro- 
cesses. 

8 



86 ELEMENTS OF CHEMISTRY. 



COMMUNICATION OF HEAT. 

It has been already said, that heat has a tendency 
to pass from one body to another, till they become 
of the same temperature. Thus, if a warm substance 
be placed near a cold one, the heat passes from the 
former to the latter, till the temperature of both is 
the same. It is now known, that heat is transmitted 
in two ways. If a hot object be placed in contact 
with a cold one, the heat passes slowlT/tromthe one 
to the other. When, on the contrary, the body is 
suspended in the air, the caloric darts off from it 
quickly to the surrounding objects. In the former 
instance it is said to be conducted ; in the latter, to 
be radiated. This necessarily divides the commu- 
nication into two parts, — the slow communication, 
and the radiation. 

Slow Communication. 

All bodies can receive heat, yet they do so with 
different degrees of celerity. If a piece of iron and 
of wood be placed near a fire, the iron will be sooner 
heated than the wood ; the same is the case with 
their rate of cooling, the former parting with its 
heat more quickly than the latter. This property of 
bodies, to receive and give out heat, is called their 
conducting power J and those which receive it, or 
part with it, quickly, are termed good conductors ^ 
while those which receive it, or part with it, slowly, 
are termed bad conductors. Though substances 
take in and give out heat differently, yet each receives 
and parts with it in the same degree. Thus, in the 
example of the iron and wood, the former becomes 
much sooner heated, but it is also sooner cooled than 
the latter. Those bodies, then, which receive heat 
quickly, also part witb it quickly, and those which 
receive it slowly, part with it slowly. 

If a rod of iron be put into a fire, the end in the 
fuel will soon become red hot, and the caloric will 



COMMUNICATION OF HEAT. 87 

pass SO speedily from particle to particle, that the 
hand cannot bear the heat of the opposite end. A 
small piece of wood, on the contrary, though burn- 
ing at one end, may be taken hold of with impunity. 

Exp. 48.- — Attach a pin, a splinter of wood, and a piece of glass 
to the end of a stick of sealing wax, so that the free extremities 
can be equally exposed to the flame of a lamp, it will be found 
that the pin will become heated, and fall off, but the glass not, 
while the wood will be consunied 

In the first instance, the metal is said to be a good 
conductor, or to communicate the heat quickly from 
particle to particle. In the latter, the wood is said 
to be a bad conductor, or to convey the heat slowly. 
Bodies, then, conductheat very differently. In gen- 
eral, the denser the substance, the more quickly 
does it conduct it. Metals, the densest bodies with 
which we are acquainted, conduct it quickly, while 
wood, earthen ware, woollen cloth, and fur, do so 
very slowly. 

That bodies conduct heat differently, may be 
shewn by a very simple experiment. 

Exp. 49. — Put a lamp under the centre of a 
sheet of copper, and at equal distances from 
the centre place a ]nece of iron, brass, lead, and 
stone, of the same size and thickness, and having 
on each a small bit of phosphorus. That on the 
brass will be first kindled, shewing that it is 
soonest heated ; in other words, that the caloric 
has passed most quickly through it. Next will come the iron, 
then the lead, and lastly the stone, the phosphorus on which will 
remain a long time. 

From experiments that have been performed on 
the conducting power of metals, it has been found, 
taking that of brass as 100, that of copper is also 
100, of iron 90. of tin 58, of lead 40. From others 
performed on a greater number of metals, it has 
been ascertained, that silver is the best conductor, 
next comes gold, then copper, tin, platinum, steel, 
iron, and lead. 



^ai, 




BS ELEMENTS OF CHEMISfRY. 

Rumford, from his experiments on the conducting 
power of porous bodies, infers, that fur and eider- 
down are the worst, and lint the best conductor, and 
the slowness with which they conduct, he was in- 
clined to think, depended, in a great measure, on the 
air which is interposed in their interstices, and the 
force with which it is retained. 

From the knowledge of the conducting power of 
bodies many useful hints are derived. When we 
wish to keep a substance warm, we surround it with 
a bad conductor, or one which allows the heat to be 
slowly transmitted through it. 

From this view of the diflferent conducting powers 
of different bodies, the fitness of different kinds of 
clothing for their respective purposes will become 
apparent. Animal and vegetable substances, in gen- 
eral, are very bad conductors; thus the hair and 
w^ool of animals, and the feathers of birds, are admi- 
rably adapted for protecting them from the cold, and 
they, moreover, enclose and retain air, which, being 
a still worse conductor, enhances the effect. For the 
same purpose we wrap our bodies in woollen gar- 
ments, and the air enclosed in their folds, greatly 
enhances their utility ; hence loose clothing is gene- 
rally warmer than that which is fitted to the body. 
This has given rise to the idea, that the woollen 
cloth, fur, &c. actually possess warmth, which is not 
the case. They merely prevent, by their bad con- 
ducting power, the air, which is colder than our 
bodies, from quickly taking caloric from them. 
When, on the contrary, we wish a substance to be 
quickly heated, w^e put it into a good conductor, as 
a metal. 

It has been already said, that the sensations of 
heat and cold, communicated by different bodies, are 
different, even though of the same temperature. 
Thus, if we put our hands on a piece of metal and 
wood, a little heated, the iron only will feel warm. 
If they be colder than the hand, the iron will feel 



COMMUNICATION OF HEAT. 89 

cold, while the wood will communicate a sensation 
very different from what it did before. This is ac- 
counted for by the difference in their conducting 
power. In the first instance, the iron, being a good 
conductor, gives off its heat quickly to the hand, 
whereas the wood, from its being a bad conductor, 
parts with it slowly. In the latter instance, the iron 
takes heat from the hand, and quickly transmits it, 
from particle to particle, so that, in a given time, it 
robs it of a great deal ; whereas the heat given by 
the hand to the wood, owing to the inferior conduct- 
ing power, remains long near the surface. The hand, 
therefore, being suddenly deprived of heat by the 
iron, feels cold ; but the abstraction by the wood be- 
ing gradual, little or no sensation is perceived. 

What has been said of the conducting power of 
bodies, and of the communication of heat through 
them, relates only to solids. The effect is very 
different with respect to liquids. In them heat is 
transmitted quickly or slowly, according to the 
method in which it is applied. In solids, it is com- 
municated from particle to particle, till the whole 
is warmed. When, on the contrary, we apply heat 
to the bottom of a vessel, with a fluid, the particles 
below, as they acquire it, expand, become lighter, 
and ascend, the colder ones fall, gain caloric and 
ascend, so that the fluid is not warmed by the heat 
being communicated from particle to particle, as 
with solids, but by its being conveyed through it by 
the currents. We should imagine, from the ease 
with which fluids are heated in this way, that they 
are good conductors; they are, however, quite the 
reverse, as has been proved by the experiments of 
Count Rumford. If a piece of ice, loaded, be placed 
at the bottom of a jar, and over this be poured cold 
water, to the depth of about an inch; and again, 
above this, boiling water, put in very cautiously to 
prevent it mixing with that beneath, the ice will con- 
tinue for a long time unm^lted, proving the very 
8* 



90 



ELEMENTS OF CHEMISTRYo 



bad conducting power of the cold wat^r. In this 
experiment, there are no currents to convey the 
caloric to the ice. 



6 



Exp. 50. — Let an air thermometer 
be cemented into a glass funnel sup- 
ported as represented ; cover the bulb 
of the instrument with water, and upon 
the surface of the water pour a small 
quantity of ether* The ether may be 
inflamed and the air thermometer will 
not be sensibly affected. 



9 





The bad conducting power of fluids is proved in 
another way, and perhaps still more satisfactorily, 
by putting at the bottom of a thin tube a piece of ice 
loaded, pouring in cold water, and applying a lamp, 
to about the middle of it, to cause it to boil. In 
this instance, the ice will remain for a long time, 
though the water, at the distance of a few inches, 
is kept boiling, and here also the currents do not 
operate, so as to afiect the ice j for though the heat 
is applied to the middle, the particles, as they are 
warmed, ascend, while the others fall, but only as 
far as the flame, where they are to gain heat, and 
rise. If, on the contrary, a piece of ice be put on 
the surface of warm water, it is almost instantly 
melted, because it is constantly washed by warm 
particles, those at the top as they give out their heat, 
contracting and falling, while the warmer ones rise 
to give out heat. 

Heat is conveyed through air in the same way as 
through fluids, and that it is so, is proved by a very 
simple experiment. 



COMMUNICATION OF HEAT. 91 

Exp. 51. — Let a person hold a red hot poker horizontally, and 
let another place his hands, one above, another below it, that 
above will be much more heated than the one below, because 
the particles of air in contact with the poker, by acquiring calo- 
ric, expand, and rise. On the contrary, if a piece of ice be held 
in the place of the poker, the hand beneath is most cooled, 
because the particles that touch the ice, by losing heat, contract 
and fall, and therefore reach the hand below. 

It is owing to the currents induced in air, by an 
application of heat, that the popular but erroneous 
idea has originated, that caloric has a tendency to 
ascend. It does not rise of itself 5 it is carried up 
by the warm air. 

From what has now been said of the conducting 
power of fluids and air, and of the mode by which 
heat is transmitted through them, many useful practi- 
cal lessons may be derived, particularly with respect 
to the economy of fuel. Thus, when we wish to 
warm a fluid, it must be heated from below, other- 
wise it will be very slowly warmed ; for, if the heat 
be applied from above, the surface only receives 
caloric, the warm particles remaining at the top. In 
throwing in heated air into a room, with the view of 
warming it, the pipes ought to open as near the floor 
as possible, to allow the air to rise, and thus commu- 
nicate heat to the whole of that in the apartment. 
In heating fluids by steam, the mouth of the pipe 
from which it issues, ought always to be near the 
bottom of the vessel, that the particles below, as they 
acquire heat by the condensation of the vapour, may 
expand and rise, and allow those above to fall, in 
their turn, to gain heat, by which the whole of the 
fluid may be quickly warmed. Were the pipe to 
terminate near the top, the particles there would 
soon become so warm, that they would cease to con- 
dense the steam ; in other words, the fluid above 
would be actually boiling, while that at the bottom 
would be quite cold. Confined air is a very bad con- 
ductor of heat; hence the advantage of double doors 
to furnaces, to prevent the escape of heat ; and of a 



92 ELEMENTS OF CHEMISTRY. 

double wall, with an interposed stratum of air, to an 
icehouse, which prevents the influx of heat from 
without. Hence, also, the origin and utility of 
double doors and windows to dwelling houses and 
apartments. 

The currents in fluids and airs serve important 
purposes in the economy of nature; indeed, science 
has no where disclosed a better proof of the existence 
and benevolence of an all-wise Creator. Thus, deep 
lakes are not frozen, though ice is formed in small 
collections of water, and there are many accounts of 
warm lakes never freezing, which has been ascribed 
to their having warm springs in them. It is to be 
accounted for, however, by the currents induced by 
a change of temperature. Suppose a lake at 50^, 
and cold is applied to the surface, the cooled parti- 
cles descend, and the warmer rise by which the 
whole of the water must be brought to a certain 
temperature ; but our common frosts do not continue 
long enough to do this, consequently, large lakes do 
not freeze. 

On the contrary, in small pools, though the cold 
applied to the surface is the same, the whole of the 
water is soon cooled to the proper degree, and ice is 
formed. 

The whole of the water, it was said, must be cool- 
ed to a certain temperature ; it is not necessary, 
however, that it must be all brought down to the 
freezing point. Owing to water, at a certain tem- 
perature, being an exception to the general law of 
expansion, (see page 65), when that in a lake is cool- 
ed to 40° by the farther abstraction of heat, the 
particles on the surface do not contract; they expand, 
and remain above, so that they are brought to the 
32d degree, and freeze, while the water below is still 
at 40°, and continues nearly so ; for the ice being a 
bad conductor, the heat is slowly abstracted through 
it. Large lakes, then, not only seldom freeze, but 
if they should, ice is formed only on the surface* 



COMMUJSICATION OF HEAT. 93 

Had not nature deviated in a remarkable degree 
from the general law of expansion, at the tempera- 
ture mentioned, the whole would be frozen when 
properly cooled, and thus prove destructive to the 
life of its inhabitants. 

The distribution of heat is in a great measure 
regulated by these currents. Thus, the earth being 
warmed by the sun's rays, imparts caloric to the air 
immediately over it, the particles of which ascend, 
and cold ones supply their place, so that, though the 
earth is constantly receiving heat, yet it is also con- 
stantly parting with it. As that part of the globe 
at the Equator is warmest, the air over it is much 
heated, and rises, so that there is a continual cold 
current from the North and South Poles towards it, 
and corresponding warm ones from the equator to 
the poles, by which the intense heat of the former, 
and severe cold of the latter, are moderated. 

The currents in fluids serve the same useful pur- 
poses. When a cold wind passes over the surface of 
water, warmer than itself, it receives heat from the 
particles above, which, as they become cold, descend, 
and have their place supplied by others, also to give 
off heat. By this means there is a constant supply 
of warmth to the air, and the cold is diminished. 
Hence, the comparative mildness of islands sur- 
rounded by a great extent of ocean, as is the case 
with Great Britain, the temperature of which is far 
above that of inland countries in the same latitude, 
the wind which reaches the former receiving heat 
from the water, whereas that coming to the latter, 
flowing over the earth, which is a bad conductor, 
receives little from it. Thus, in many parts of the 
Russian dominions, in the same latitude as that of 
Britain, mercury is often frozen during winter, so 
that the thermometer must be at least 40° below 
zero, whereas, in Britain, it is rarely so far down as 
10°, almost never to 0°. 



94 



ELEMENTS OF CHEMISTRY. 



Eadiation. 

When a warm object is suspended in the atmos- 
phere, the caloric flies off from it to the surrounding 
colder bodies with great velocity. If a person place 
his hand before a hot substance, but with a screen 
between them, he is not warmed, but the moment 
the screen is removed, he is sensible of the heat. 
This shews the quickness with which it passes 
through the air ; hence it is said to be radiated. 
The rays that thus dart from warm bodies, may be 
reflected and concentrated into a focus. Thus, if a 
person stand at the side of a fireplace, he is not 
warmed ; but if a polished plate of metal be held 
opposite it, the rays passing from the fire, and strik- 
ing the plate, are reflected, and, if properly directed, 
will reach the person, and warm him. 

To illustrate the different facts concerning radia- 
tion, polished metallic concave mirrors are employ- 
ed, some of which are sections of an oval, others of 
a" circle, or an ellipse. If they be placed opposite to 
each other, at the distance of several feet, a cage of 
charcoal near one will instantly affect a thermometer 
in the focus of the other. There is no necessity, 
however, for having recourse to so delicate an indi- 
cation of the heating effect ; for if a piece of phos- 
phorus be held in the focus, it is soon kindled. 

In these experiments, there must be something 
emanating from the charcoal, which is reflected by 
the mirrors, and concentrated also into a focus, so 
as to set fire to phosphorus. When, then, the char- 
coal, is placed near the mirror a, rays of heat fly off 
from it in straight lines, to the mirror, by which 





RADIATION. 95 

they are instantly reflected again in straight lines, to 
the opposite one h^ where they are also reflected, 
and are thus brought to a point at c, where the heat- 
ing efiect is produced. The distance at which this 
takes place, depends of course on the form of the 
mirror. If, instead of burning charcoal, we make 
use of a red hot iron balJ, the same is produced, 
though the efiect is not so great, the temperature of 
it being less than that of the other, 

Some objects have the power of absorbing, others 
of allowing the rays to pass through them. Thus, 
if a pane of glass be placed between the mirrors, the 
heating efiect is not produced, because it retains the 
rays. It is owing to this that we can look through 
glass at a strong fire, or furnace, without hurting 
the eye, the rays thrown ofi" being prevented from 
reaching it. Other bodies, on the contrary, reflect 
the rays. Thus, if we cause them to strike on a 
polished one, little heating efiect is produced. If a 
diflerential thermometer, with its ball gilded, be put 
into the focus of one mirror, the cage of charcoal 
into the other, there is very little efiect on it, the 
rays that strike it being instantly reflected. On the 
contrary, if the other ball be blackened, and placed 
in the focus, the change is much greater, the black- 
ened surface absorbing the rays. Some bodies 
therefore absorb, while others reflect the radiations 
of heat. 

The above remarks apply to burning and incan- 
descent bodies. The same, however, is the case 
with substances not incandescent ; these also, if their 
temperature be above that of the atmosphere, are 
constantly giving forth heat ; and that they do so is 
proved, by placing any warm object, as a flask of 
boiling water, near the mirror; the thermometer in 
the focus of the other is instantly afiected, thus prov- 
ing, that all objects, the temperature of which is 
above that of the contiguous ones, are sending ofi* 
radiations of caloric. 



96 ELEMENTS OP CHEMISTRY. 

Having made these preliminary observations, we 
have now to state more particularly the different 
facts concerning radiation. The power of radiating 
is proportional to the difference between the tem- 
perature of the hot body, and the surrounding me- 
dium, and also to the extent of surface. 

The most remarkable circumstance, however, is 
the effect of the nature of the surface. It has been 
ascertained, by numerous experiments, that the more 
resplendent the surface, the less is the radiation ; 
and on the contrary, the darker and rougher it is, the 
radiating power becomes the greater. The effect 
of surface is well illustrated, by putting different 
flasks near the mirror. If a flask with a resplendent 
surface be filled with boiling water, and put near 
the mirror, the thermometer is \ery little affect- 
ed ; but if the same flask have its surface smoked, 
the effect becomes much greater. The power of ra- 
diating has been well illustrated by the experiments 
of Leslie. He took a cannister of tinned iron, cov- 
ered one side with smoke, a second with paper, a 
third with glass, and left the fourth resplendent. It 
was filled with boiling water, and placed with its 
sides towards the mirror. Considering the effect of 
the black side on the thermometer as 100, that of the 
paper was 96, of the glass 90, and of the resplend- 
ent metallic one only 12; so that blackened objects 
produce about 8 times as much effect as resplendent 
ones. 

It has been already remarked, that bodies receive 
the rays very differently. The experiments with the 
differential thermometer already mentioned, shew 
that blackened bodies receive them very quickly, 
while resplendent ones scarcely receive them at all ; 
in other words they reflect them. Those bodies, 
then, which are good radiators, are good absorbers ; 
while those which radiate little, absorb little. Good 
radiators, therefore, are bad reflectors, and bad radi- 
ators are good reflectors. 



RATE OF COOLING. 97 

Frc .1 what has now been said, we see that heat is 
communicated in two diflerent ways, — the one by 
slow communication from particle to particle, — the 
other by its darting through the air from the surface 
of one object to another. When, then, a hot body is 
placed in air colder than itself, both of these modes 
operate; but they do so very differently, — one los- 
ing most by communication, another by radiation. 
Even the same substance, at different times, parts 
with its heat differently, according to circumstances. 
In general, that given out by the one method, is in- 
versely to that lost by the other, — that is, when 
much is lost by communication, there is little emitted 
by radiation ; or if much is given forth by radia- 
tion, there is little loss by communication. Thus 
good conductors, for instance metals, are bad radi- 
ators. Spongy bodies conduct heat slowly, but 
they radiate powerfully. The cooling and heating 
process is also much influenced by external circum- 
stances : these refer both to the bodies themselves, 
and to the medium in which they are placed. To 
the former belong temperature, size, figure, surface, 
and the peculiar nature of the body. It is a general 
law, that the greater the difference of temperature 
between the hot body and cooling substance, the more 
quickly it loses caloric. Thus, if we have two 
masses of the same matter, but of different sizes, the 
heat given out is not in proportion to the quantity 
of flatter, but to the surface. Suppose we have an 
inch cube and two inches cube of the same substance, 
and at the same temperature, the latter contains eight 
times as much matter as the former; but it does not 
lose, in the same time, eight times as much heat, — 
it gives out only four times as much, because it pre- 
sents four times the surface. It follows from this, 
that the figure must also affect the cooling, as it varies 
the extent of surface. If we have two objects of the 
same nature, that which exposes most surface, cools 
9 



93 ELEMENTS OF CHEMISTRY. 

most quickly. A sphere, therefore, which presents 
least, cools more slowly than any other. 

The effect of the surface in influencing cooling, has 
been already explained when detailing the laws of 
radiation.* The darker and rougher, the more pow- 
erfully does it radiate ; it must therefore cause an 
object to cool more quickly. On the contrary, the 
more resplendent the surface, the less does it radiate ; 
it must therefore make a body cool the more slowly. 

The nature of the object itself also affects the cool- 
ing, more particularly with respect to its conducting 
power. A good conductor, as a metal, cools much 
more quickly than a bad conductor, as wood ; be- 
cause the heat which is carried off from the surface 
of the former, is soon supplied from the internal 
parts ; whereas in the latter, it passes slowly from 
within, to supply that taken from the surface. 

The cooling process differs, also, according to the 
nature of the substance by which the warm object is 
surrounded. The more heat it can receive, the 
more quickly is the other cooled. A substance, also, 
which is a good conductor, cools a body more speed- 
ily than one which is a bad conductor, because the 
heat given off from the latter is quickly communicat- 
ed from particle to particle, so that, in a given time, 
it loses a great deal of heat. Thus, a hot iron cools 
more quickly in water than in air, and much sooner 
in quicksilver than in water, — water being a better 
conductor than air, and quicksilver better than water. 

Air, it has been said, is a bad conductor, and cools 
a body slowly. If, however, by any means the par- 
ticles which are heated be removed, and others made 
to supply their place, the cooling goes on more 
quickly. Hence the effect of wind in accelerating 
it; a substance being much sooner cooled dur- 
ing a breeze than when the air is cahn, as is well 
exemplified in our own persons, a windy day always 
feeling colder than a calm one, though of the same 
temperature, because the wind carries off the warmer 

* See Manual, p. 33. 



RATE OF COOLING. 99 

particles of air, and supplies others, which also de- 
prive us of heat, whereas in a calm atmosphere, the 
air that has taken heat from us is retained in a great 
measure among our clothes. Hence it is, also, that 
when carried quickly through the atmosphere, we 
feel so cold, as when driving in a gig, the air with 
which we are constantly brought into contact de- 
priving us of heat, while we have no exercise as a 
means of supplying the loss. 

What has been said of the cooling, applies equally 
to the heating of bodies, for those which give out 
much heat by radiation, so as to cool quickly, re- 
ceive it easily, so that they are soon heated ; while 
those which radiate little receive few of the rays of 
heat, and are slowly w^armed. On the other hand, 
those which cool quickly by giving out caloric by 
communication, take it in quickly in the same way, 
and are soon heated : while those which communi- 
cate slowly receive little by communication. 

From W'hat has now been said concerning the 
communication and radiation of heat, and of the 
circumstances that influence the heating and cooling 
of bodies in these different ways, many useful practi- 
cal observations may be drawn. Water continues 
much longer warm in a resplendent than in a blacken- 
ed vessel. Hence metallic ones, with their surfaces 
polished, are employed for holding warm water, 
when we wish it to retain its heat for some time. It 
is a common remark, that tea is more easily infused 
in a silver than in an earthen tea-pot, which was at 
on^ time supposed to be owing to some property of 
the metal itself, but which is now accounted for by 
the laws of radiation, the bright metallic surface giv- 
ing forth fewer rays than the other, and, of course, 
cooling the water less slowly. A metal is, however, 
a good conductor; it is of advantage therefore, to 
have not only a bad radiator, but also a bad conduc- 
tor, that the heat given off from the surface by radia- 
tion, may be slowly supplied from the interior. 



100 ELEMENTS OF CHEMISTRY. 

Hence the frequent use of earthen ware covered 
with metallic matter, for iiolding warm fluids, as for 
jugs and tea-pots, the earthen ware being a bad con- 
ductor, and, by having its surface resplendent, be- 
coming also a bad radiator, by which little heat is 
given off. 

When, on the contrary, we wish to cool a- fluid 
quickly, it must be put into a vessel which is a good 
conductor, as a metallic one, and with its surface 
blackened, to make it a good radiator. In convey- 
ing heated air, or steam, from one place to another, 
with the view of heating apartments, the tube ought 
to be made of bright metal, as tinned iron, that there 
may be little heat lost before the air reaches the 
place to be warmed. When, on the contrary, the 
steam is to be condensed, the tubes ought to be made 
of blackened metal, as sheet iron, so that a great 
deal of caloric may be given ofl", both by radiation 
and by communication. 

When we have to guard a body from heat, we 
cannot employ a better protector than a plate of 
bright metal. Thus, in erecting a stove near wood- 
work, the latter ought to have a sheet of tinned iron 
placed near it, but not in contact with it, by which 
the greater part of the rays sent ofi* from the stove 
are reflected. Should the metal itself become warm, 
the layer of air between it and the wood, being a 
very bad conductor, prevents in a great measure the 
transmission of the heat. Should stone be employed 
as the protector, it must be whitened, so that it may 
absorb as few of the rays as possible. 

Before finishing this subject, we may here take 
notice of some beautiful provisions of nature, for pre- 
venting too great heat or cold over the earth. 

It has been shewn, that when a warm object is 
placed in the air, it is constantly giving forth radia- 
tions. Gould we suppose, then, an object to be send- 
ing off'rays, without receiving any to compensate for 
the loss, it would become cold. This is actually the 



HOAR-FROST AND DEW. 101 

ease with the earth during night. The prhicipal 
source of the earth^s heat, is the sun's rays, which, 
passing through the air without warming it, arrive 
at the earth and are absorbed. During night this 
gives forth radiations, which fly up in the atmos- 
phere ; and, as it does not receive any in turn, its 
temperature falls. By this fact, many curious oc- 
currences of nature can be satisfactorily accounted 
for. It has been already fully illustrated, that dur- 
ing the conversion of a vapour to fluid or solid, heat 
is disengaged. The deposition of hoar-frost and 
dew, which are merely the condensed watery 
vapour of the atmosphere, was, however, considered 
a remarkable exception to this. 

It was observed at Glasgow, that a thermometer 
hung in the air was at — 7, while one placed on the 
ground was so low as — 23. This, however, was 
the case only when the air was calm, and the sky 
clear ; when a cloud was passing, the temperature of 
the instrument on the ground instantly rose, but 
again sank when the sky was unobscured. The same 
occurred with rough bodies, as grass, and leaves of 
plants, the thermometer, when placed on them, in- 
dicating a much lower temperature than one hung in 
the air. When, however, the former was placed on 
a polished object, as a plate of metal, there was no 
difference, the temperature of both being the same. 
It was found also, that though the thermometer on 
the ground was acquiring hoar-frost on its bulb, its 
temperature was considerably lower than that of the 
other, and on which there was no hoar-frost. Novv^ 
this is the reverse of what should have happened ; 
the watery vapour, during its conversion into hoar 
frost, ought to have raised the thermometer; it ap- 
peared, therefore, to be a deviation from the general 
law. It has now, however, been proved by most 
satisfactory experiments, that this is not the case ; 
the cold, it has been shewn, is not the consequence, 
but the caicse of the deposition. During a calm and 
9* 



102 ELEMENTS OF CHEMISTRY. 

clear nighty a thermometer on the ground will be 12 
degrees lower than one hung in the air, and which 
is occasioned by the earth radiating caloric, which 
passes off into the heavens ; as there is nothing to 
return heat, its temperature, and consequently that 
of the instrument on it, sinks. But if the sky be 
clouded, or if a screen be placed over the instru- 
ment, the cooling effect does not go on ; because 
though the earth is radiating as before, it receives 
rays from the clouds or screen, to compensate for the 
loss. When, then, the air is calm, and the heavens 
unobscured, cold is produced, and hoar frost, or dew, 
is deposited, the earth cooling the air in contact with 
it, and thus depriving it of the power of holding the 
watery vapour in solution; the cold therefore, inva- 
riably j^rece^/e^, and is not, as was originally suppos- 
ed, the consequence of the deposition. 

Those bodies that radiate most powerfully , as grass, 
twigs, cotton, and woollen cloth, become coldest, and 
on them hoar frost is deposited ; while on the re- 
splendent bodies, as there is little radiation, there is 
scarcely any deposition. It is on this principle that 
we can explain, why two thermometers, having 
different surfaces, will indicate different degrees of 
cold during night. If the one be resplendent, as 
when filled with mercury, it gives forth few radia- 
tions, so that its temperature is little reduced; but if 
the other be blackened, owing to its becoming a good 
radiator it loses more heat than the other, and, as 
neither is receiving any, its temperature is more re- 
duced. For the same reason, also, a differential 
thermometer, with a transparent and black ball, in- 
dicates cold in the stem of the latter, when exposed 
during a clear night, by the black one giving forth 
more caloric than the latter. 

The radiation of heat during night, serves impor- 
tant purposes in the economy of nature. Were it 
not for the rays given forth from the earth, after 
sunset, it would be heated to an intolerable pitch, by 



CALORIC IN BODIES. 103 

the constant absorption ; whereas, by radiating at 
night, heat is abstracted, and the temperature is thus 
kept nearly uniform. In the vegetable creation, it 
is also of the utmost advantage. During dry weath- 
er, vegetation would cease for the want of water, 
but vegetables, from the nature of their surface, are 
well adapted for radiating heat ; hence, in a clear 
and calm night, owing to the cold produced by the 
radiation, the moisture in the atmosphere is condens- 
ed, and deposited in the form of dew or hoar frost, 
which not only supplies them with water, but also, 
by the disengagement of heat during its formation, 
prevents the bad effects that would otherwise be oc- 
casioned by the radiation, so that the cold is the 
means of supplying them with water, and the forma- 
tion of the water replaces the neat that was given out 
to produce it. 

OF THE RELATIVE QUANTITY OF CALORIC IN BODIES. 

It has been already mentioned, that caloric has a 
tendency to pass from one body to another, till all 
become of the same ternperahire ; we are not, 
however, to infer from this, that they contain the 
same quantity; indeed, we shall find that it is very 
different. Thus if we take 20 pounds of water, and 
divide it into two parts, one containing 19, the other 
1 pound, on applying a thermometer, they will be 
found to be of the same temperature; it is evident, 
however, that they contain different quantities of cal^ 
oric; the one must have just nineteen timesas much 
as the other. Different quantities of the same matter^ 
then, have different quantities of heat. The same, 
we shall find, is the case with equal quantities of 
different bodies ; and that it is so, can be proved 
also by experiment, as by mixing thern at different 
temperatures, and marking the heat of the mixture. 
If the substances produce by their union a onean 
temperature, we must infer that the caloric in each 
is the same ; because that taken from the one, and 



104 



ELEMENTS OF CHEMISTRT. 





transferred to the other, has lowered it as many de- 
grees as it has raised the other ; but this is very 
rarely the case, — the temperature is either above or 
below the mean. 

Exp. 52.—Thus if equal 
weights of warm mercury 
and cold water be mixed in a 
jar, A, they do not produce 
a mean heat ; it is far below 
it. Suppose that the tem- 
perature of the mercury is ^ 
156, and of the water 40, ^^ 
that of the mixture is not the 
mean 98, it is only 44. Here, 
then, the mercury has lost A 

112^, but the water has gained only 4^. Again, if equal 
equal weights of warm water and cold mercury be mixed, the re- 
sulting heat is above the mean. Suppose, as before, that the wa- 
ter is 156, the mercury 40, the temperature of the mixture is not 
the mean 98 ; it is 152. In this instance, the water has lost only 
4Q, but the mercury has gained no less than 112^. 

In these experiments, the caloric which has raised 
or depressed the temperature of the mercury 112 
degrees, has affected that of the water only 4, or 
l-28th part. Hence, the latter requires 28 times as 
much as the former, to elevate its temperature to the 
same height; and, if so, it must contain 28 times as 
much. 

That bodies contain different quantities of caloric, 
is proved also by adding different quantities to the 
same weights of them ; and to procure equal quanti- 
ties of heat, we have merely to use always the same 
measure of boiling water, provided this does not act 
chemically on the substance to which it is added* 

Exp. 53. — On the addition of a 
measure of warm water to the jar 
W, containing a pound of water at 
50, the temperature will rise, say 10 
degrees. — On adding a similar measure 
to O, having a pound of sperm oil, it 
will rise 20** ; and the same addi- 
tion to G, in which there is a pound 
of powdered glass, will cause a rise to 
50«. 




CAPACITIES OP BODIES. 105 

Here then equal quantities of caloric added to wa- 
ter, oil and glass, have raised the temperature of the 
first 10, of the second 20, and of the third 50 de- 
grees. If we wished to raise them all the same 
number of degrees, say 50, it is evident that we must 
add twice and a half as much to the oil, and five 
times as much to the water, as to the glass. If so, 
oil must contain twice and a half as much, and water 
five times as much as the glass; the quantities of 
caloric in them are, therefore, as glass 10, oil 20, 
water 50 ; or, taking water as the standard, calling 
it 1000, they are, water 1000, oil 500, glass 200. 
The same is the case with all other substances, the 
caloric necessary to raise the temperature to the same 
height, varying in almost every difierent instance ; 
hence, they are said to have difierent capacities for 
it. By the term capacity for caloric, then, is meant, 
the power which bodies have of receiving it, by 
which their temperature is to be afiected, some more 
than others. 

Though it has been thus proved, that bodies have 
difierent capacities for caloric, of course, have difier- 
ent quantities of it, yet we know nothing of the «c- 
fual quantity, we speak of it merely comparatively. 
It is necessary, therefore, to have some substance as 
a standard, and to which all others can be referred. 
For this purpose, water has been fixed on for solids 
and fluids, and air for gases, and called 1000. If, 
then, the capacity of any body be 2000, it means 
that, weight for weight, it will require twice as much 
to raise its temperature to the same height as water 
does.— jPor the capacities of different bodies, see 
Appejidix.^ 

*\n raferring to that table, the numbers must be considered as pointing out the re- 
lative quantities of caloric in the bodies, and, of course, the effect that equal addi- 
tions would produce. Thus, the capacity of water being 1000, that of mercury is 
'28, by which we are informed, that at any temperature, the caloric in water being 
taken as 1000, that in mercury at the same temperature is only 28. Hence, we are 
also informed, that if equal "quantities of caloric were added to them, the rise of 
temperature would b-^ inversely as 1000 to 28, that is, 1 to 36 ; consequently, if we 
wished to raise th?ir to the same degree, we must add 36 times as much to the water 
as to the mercury, and hence the principal practical aj^iicatiou of a knowledge of 
the capacity of different bodies. 



106 ELEMENTS OF CHEMISTRY. 



^VARIATIONS OF TEMPERATURE. 

From the tendency which heat has to diffuse itself 
through bodies, till there is an equality of tempera- 
ture, it would soon be established over the earth, 
were it not for the operation of foreign powers, which 
are constantly at work. The changes that occur, are 
however, not great, the extremes of heat and cold 
that w^ould otherwise ensue, being prevented by the 
same powers. 

We do not find the range of natural temperatures 
very extensive. The average heat of the globe is 
about 50, the extremes not being many degrees above 
or below this. In w^arm climates, the thermometer 
occasionally stands at 110 or 115 in the shade, while, 
in the colder regions, it sometimes falls to 50 below 
the beginning of the scale, thus making a range of 
about 160 or 170 degrees. The range of tempera- 
ture which we can procure by artificial means, 
is luckily mpch greater than this, the lowest cold, 
accurately measured, being — 91, or 123 below the 
freezing point, while the greatest heat, also accurate- 
ly ascertained, was considered to be at least 21,000. 
Higher and lower degrees have been produced, 
but the temperature of these has not been ascer- 
tained. 

The different means of generating heat, applied to 
useful purposes in the arts, are Ist, Mechanical ac- 
tion between solids, as Friction and Percussion ^ 
and 2d, Chemical action^ under which is included 
the most important of the whole, Combustion. 
The sources of cold are. Evaporation and Chemi- 
cal action^ 

MEANS OF GENERATING HEAT. 

During friction there is a considerable rise of tem- 
perature, as is well illustrated when a piece of phos- 
phorus; is rubbed^ the heat evolved being sufficient 



MEANS OF GENERATING HEAT. 107 

to set it on fire. By rubbing two pieces of wood 
together, combustion is often excited. Thus, the 
inhabitants of the South Sea Islands avail themselves 
of this for kindling their fires. They have two 
pieces of wood, one passing through a hole in the 
other, to which it is accurately fitted, and by causing 
it to turn quickly by means of a cord, the heat is 
sufficient to kindle them. In this way forests have 
been burned by the violent friction of the branches 
against each other during storms. The wheels of 
machinery, and ships, also, by the rubbing of cables 
against the sides during the lowering of the anchors, 
have been set on fire. The temperature produced 
in these instances does not depend on the hardness 
of the bodies employed, as it is generally remarked 
that the softest woods occasion the greatest heat. 

The heat excited by percussion is equal, in many 
cases it is superior, to that evolved by friction. If 
a piece of iron be struck against flint, or two flints 
against each other, small sparks are thrown off. A 
familiar instance of the generation of heat by per- 
cussion, is the method a blacksmith often resorts to 
for kindling a fire. He places a small rod of iron 
on the anvil, and strikes it repeatedly and forcibly 
with his hammer. In a short time it becomes so 
hot, that a sulphur match may be easily kindled 
by it. 

Under the production of heat by mechanical means, 
may be mentioned the method of generating it by 
suddenly condensing atmospheric air. In working, 
the syringe, by which this is compressed into an air 
gun, it is always found to become warm. In this 
case, much of the heat evolved must depend on fric- 
tion ; a sufficiently high temperature can, however, be 
produced by the sudden compression of air, to set 
fire to inflammable bodies. On this depends the in- 
stantaneous light-giving syringe, for affording a light. 
It is merely a small brass tube, to which a piston is 



108 ELEMENTS OP CHEMISTRY. 

accurately adapted, and at the end of which, there 
is a cavity for containing the tinder. That employ- 
ed is the substance called Amadou^ which is a fun- 
gous excrescence growing on some trees, and beat 
till it becomes quite spongy, and afterwards soaked 
in nitre. A little of it is placed in the cavity at the 
end of the piston, which is put into the syringe, and 
driven forcibly home, and the heat evolved during 
the sudden compression of the air is sufiicient to 
kindle it. 

The most abundant source of heat, and that appli- 
ed to the most useful purposes, is Chemical action. 

By the mixture of different substances, a chemical 
action is induced, which is generally accompanied 
with a change of temperature, frequently with the 
evolution of caloric. Thus, when oil of vitriol and 
water, in equal quantities, are mixed, a sufficient 
heat is excited to set fire to inflammable matter. 

Exp. 54. — If, for instance, some tow, with a piece of'phospho- 
rus m it, be wrapt round a thin phial, and the above named mix- 
ture be made in it, the tow is scon kindled. 

Exp. 55. — Mix, cautiously, a small quantity of sugar with 
about half its weight of the salt called chlorate of potassa ; drop 
upon the mixture from the extremity of a glass rod a little sul- 
phuric acid ; it will be inflamed. 

Dead animal and vegetable matter under certain 
circumstances, undergo a change q,2\\^^ putrefaction^ 
during which heat is evolved. This mode of pro- 
ducing it is resorted to only by farmers and garden- 
ers. Horse dung, and oak-bark after being used by 
tanners, are the substances generally employed. The 
former, when there is a large collection of it, will 
excite heat of about 140°, which it continues to do 
for a long time ; hence its use by gardners in mak- 
ing hot-beds. Tanners' bark is employed also for 
the same purpose. 

The last, and by far the most important source of 
heat, is combustion. Before proceeding to treat of 
the generation of heat by it, it uiay be remarked, that 



MEANS OP GENERATING HEAT. 109 

it is occasioned by a chemical action between an in- 
flammable body and the air of the atmosphere; of 
course, a supply of the latter is absolutely necessary, 
and the more freely it is admitted, the more rapid is 
the combustion. On this depend many of the im- 
provements which have lately been introduced for 
increasing the heat during this process. Till within 
a short time, the only inflammables were solid or 
fluid, hut of late an aeriform substance has been used, 
with w^hich a most intense heat can be excited. The 
fluid combustibles are oil and tallow, for the latter, 
though solid at a natural temperature, is liquefied 
before it is burned. It is of great consequence, in 
the combustion of these, that the heat be steady, 
and that there be no unnecessary waste of the mate- 
rials; for this reason it is usual to burn them on a 
soft combustible, as cotton, by which the fluid is 
drawn up, and gradually consumed. In the case of 
tallow, the heat given out by the burning of the cot- 
ton, and afterwards by its own combustion, melts it, 
and thus allows it to be burned in the same way a3 
oil. The flame caused by the combustion proceeds 
from an inflammable air given out, which unites with 
part of the air of the atmosphere : where this is not 
in contact with it, it is of course not consumed, and 
hence the cause of smoke, which is merely the char- 
coaly matter that exists in the gas, deposited from it 
in the state of very fine powder. To prevent this, 
three different methods are adopted. Ist^ To use a 
very small wick. 2d, to have a flat wick, as is com- 
monly employed in kitchen lamps. 3d, To have the 
wick hollow, which is by far the greatest improve- 
ment that has been made. This was recommended 
by Bolton, but introduced by Argand, and hence 
lamps with it are called Argands. 
10 



110 



ELEMENTS OP CHEMISTRY. 




By using a hollow wick, there is a constant cur- 
rent of air through it, entering at A, by which the 
whole of the flame is brought into 
contact with it, and the inflam- 
mable matter is consumed, and 
smoke prevented. To increase the 
draught through the wick, it is ne- 
cessary, also, to surround it by 
a cylinder, B, by which the air 
is more freely supplied, and the 
combustion more complete. C is ' 
the part of the lamp for holding the oil, which is con- 
veyed by the tubes D and E to the wick in F. Though 
this mode of consuming oil is employed principally 
for afibrding light, yet it is a good method of supply- 
ing heat, particularly to small vessels. n using it for 
this purpose, the wick is surrounded by a copper cyl- 
inder. By placing a cylinder over a common lamp, 
the flame becomes much steadier, and the smoke is 
in a great measure prevented, so that this, also forms 
a good mode of applying heat on a small scale. 

For experiments in the small way, 
spirit of wine is the neatestand most 
convenient fuel, and hence the spirit 
lamp may be employed for most ope- 
rations of analysis as a very conve- 
nient furnace. 

It has been already said, that the renewal of air 
is absolutely necessary for combustion, and the more 
freely it is admitted, the more rapid is the consump- 
tion of the combustible ; hence the heat may be 
greatly increased by causing a blast through the 
flame. For this purpose, a blow-pipe, to be blown 
either by the mouth or by bellows, is used. It is 
of very little consequence what form of pipe is 
adopted, though different kinds have been recom- 




MEANS OF GENERATING HEAT. Ill 

mended by different people. This is the 
> form of the common blow-pipe, the ball a, 
being intended to condense the moisture in 
the air coming from the lungs. By causing 
air to pass through the flame, it is drawn to 
a fine point, d, at which a most intense heat 
is excited. In using the lungs as the means 
of procuring the blast, when these are nearly 
exhausted of air, the mouth must be filled by 
distending the cheeks ; and by afterwards 
compressing these, the air is expelled through 
the pipe, while it may at the same time be 
taken in through the nostrils, so that a con- 
tinual blast can be kept up for a long time. 
When the lungs cannot be used, recourse is had to 
double bellows. 

The principle on which the blow pipe acts, is by 
bringing a constant supply of air to the inflammable 
matter, thus rendering the consumption more com- 
plete, and the consequent heat greater. 

The next class of combustibles is the solids. These 
are wood, charcoal, peat or turf, and coal. In those 
countries in which wood abounds, it is the principal 
fuel. Its combustion is lively, but it gives out a 
great deal of smoke and flame, which render it unfit 
for many operations. When wood is converted to 
charcoal J these inconveniences are prevented, and it 
is then useful, as a means of generating heat, for 
many purposes of the arts. In this way it is used by 
dyers, confectioners, and many others. It is also 
much used by chemists. Peat, or dried turf, is like- 
wise used as fuel, but chiefly in those places where 
the others cannot be obtained. Coal is by far the 
most useful of the inflammables, and it is employed 
in almost every operation where an intense heat is 
required on a large scale. It is used in two states, 
either as procured from the mine, or in the form of 
cokcj which is prepared merely by exposing it to 
heat, in close vessels, to keep it from the air, by 



112 



ELEMENTS OP CHEMISTRY. 



which it is deprived of those substances that are the 
cause of flame and smoke. Coke is employed when 
heat is required for carrying on different operations. 

When fuel is burned in a grate, the heat that en- 
ters the apartment is that emitted by radiation ; the 
whole of the warm air escaping up the vent, because 
that in contact with the fuel being heated, becomes 
lighter and ascends. The more rays, then, that can 
be thrown into the room so much the better. Rum- 
ford has therefore proposed, that the side of the fire- 
place be made of some material that reflects the 
radiated heat, and that they may be so situated, as to 
throw off as many rays as possible ; hence they are 
now placed in a slanting direction, instead of being 
square with the back, as formerly. By these means 
there is not only less fuel consumed, but our apart- 
ments are better heated, and smoke is in a great 
measure prevented, because, as the fire-place is nar- 
rower, there is a greater draught up the vent. 

Coal is sometimes also burned in a stove, for heat- 
ing apartments. A stove is merely a grate, but con- 
fined on all sides, the air necessary for the combus- 
tion entering through the apertures below, in the 
ash-pit, and the smoke passing up through a tube 
from the top. In this way of burning fuel, the sup- 
ply of air is not great, consequently there is not 
much change of that in the room, which makes it 
feel disagreeable to those not accustomed to it. 

A particular modification /" IHB 

of a stove, is well adapted 
for warming large places, as 
churchesand manufactories. 
It is merely a common stove, 
A, surrounded by an outer 
covering, B, at the distance 
of a few inches, with open- 
in;£S below, C. to admit air. 
When the stove is kindled. 




FURNACES. 113 

and becomes hot, the air that enters through the 
outer part striking it, is instantly heated, and, be- 
coming lighter, ascends, being forced up by the cold- 
er air that is rushing in to supply its place. It may 
thus be conveyed by tubes, D, through the room, or 
even ta the different apartments of a building, the 
tubes being made of a resplendent metal, as tinned 
iron, so that they may give off little heat by radiation, 
during its passage through them. — (See p. 99. J 
The smoke is carried off by the vent E. 

Coke is burned in chauffers, or furnaces. A chauf- 
fer is merely a cylindrical box of sheet iron, open 
above, and with a grating at the distance of about 
an inch from the bottom, for supporting the fuel, the 
air for the combustion entering at apertures below. 
These are well adapted for applying heat to small 
vessels. By putting on a vent, or funnel the heat 
becomes very intense, and this is often used when 
we wish to apply a strong heat to substances placed 
amidst the fuel, as in crucibles. 

Furnaces are of different constructions, according 
to the use to which they are applied, but in their 
general construction they are the same. A furnace 
consists of three parts ; a body, with a grating for 
holding the fuel, an ash-pit, in which the openings 
for the admission of air are generally placed, and a 
chimney, for the escape of the smoke. There is 
also an opening in the upper part, into which a pot 
for holding sand can be placed. In this way heat is 
applied very equally when we wish to carry on 
distillation. 

Furnaces on a large scale are of the same general 
construction ; a body for holding the fuel, an ash- 
pit, and a vent, — but different forms are used, accord- 
ing to the use to which they are applied.* 

The combustion in furnaces, and the consequent 
heat, depend on the supply of air to the burning 

* See Manual t plate ix. 

10* 



114 ELEMENTS OF CHEMISTRY. 

body. The quicker its renewal, the more rapid the 
combustion, and, of course, the more intense the 
heat. The rapidity with w^hich the air is made to 
enter, is increased in two ways, either by enlarging 
the openings for its admission, or by lengthening the 
chimney. When it is required that the heat should 
be very strong, the vent is carried to a great height, 
by which the air is made to enter rapidly, and the 
fuel is quickly consumed. This is occasioned by 
the air in the vent being lighter than that without ; 
it therefore rises to make way for its admission 
below. So long, then, as the air in the vent is 
enlarged, it is pressed up by the heavier colder 
particles. When, however, the chimney is so long 
that the air within and without are of the same den- 
sity, there is no farther increase of the rapidity with 
which it enters, though the vent is made higher. 
The longer, then, that the air can be kept warm, so 
much the better, because it is expanded, and lighter 
than that without. Hence chimneys, even though 
short, are made of bad conducting materials, to allow 
the air in them to cool slowly, — in other words, to 
contract slowly. 

In the construction of furnaces, it is of the utmost 
consequence that the heat be as much confined as 
possible. On a large scale, they are made of bricks, 
and sometimes lined with fine clay. Smaller furna- 
ces, as those made of metal, are always lined with a 
mixture of clay and sand, or w^th charcoal and clay, 
and afterw^ards with clay and sand, to protect the 
charcoal from the fire. This not only confines the 
heat, but prevents the destruction of the furnace. 

MEANS OF GENERATING COLD. 

It must be kept in mind, that by generating cold, 
is meant merely the abstraction of caloric. The 
sources of cold are, Evaporation and Chemual 
action. 



MEANS OF GENERATING COLD. 115' 

It has been already fully explained, when treating 
of evaporation^ that when a fluid is converted into 
vapour, it absorbs caloric. — {See page SO.) If this 
be not supplied, it must take it from itself, or from 
any body in contact with it, and hence generates 
cold. When, for instance, the hands are wetted, 
and exposed to the air, they feel cold, because, dur- 
ing the evaporation of the water, it absorbs heat 
from them. That cold is generated by this pro- 
cess is proved also by covering the ball of an air 
thermometer, with muslin, and pouring a little 
alcohol or ether on it; the fluid in the stem 
instantly rises, owing to the contraction of the 
air in the ball, and thus indicating cold. If the 
ball of a common thermometer, after being 
covered with muslin be dipt in ether, and 
whirled in the air, its temperature falls consid- 
S erably. 

It has been already proved, that as the pressure 
on a fluid is diminished, it evaporates more easily 
than when exposed to the air. Hence a method of 
increasing the rapidity of the evaporation, and con- 
sequent reduction of temperature. 

Exp. 40, — Immerse a tube, containing water at the bottom, in 
a glass of ether, which is to be placed under the receiver of an 
air pump ; or the ether may be allowed to float on the surface of 
the water. During the exhaustion of the vessel, the ether will 
evaporate rapidly, and, robbing the water of heat, will completely 
freeze it; thus exhibiting the singular spectacle of two fluids in 
contact with each other, one of which is in the act of boiling, 
snd the other of freezing, at the same moment. 

In this experiment the vapour formed, itself exerts 
a pressure on the water ; unless, therefore, we keep 
constantly working the pump, the evaporation ceases. 
There is an easy method, however, of condensing 
the vapour, which is to place a vessel with oil of 
vitriol under the receiver, which owing to its power- 
ful attraction for water, condenses the vapour as it- 
comes off; and thus keeps up the vacuum. We are 




116 ELEMENTS OF CHEMISTRY. 

indebted to professor Leslie for this method of gene« 
rating cold. He places on the plate of the pump, at 
basin with oil of vitriol, and over this 
a small unglazed earthen-ware dish, 
with water, resting on a stand. The 
receiver, is then put on, and exhausted. 
The water being under less pressure 
than before, evaporates, and the vapour 
is quickly condensed by the acid, so 
that the vacuum is kept up, the evapo- 
ration continues, and the vapour, during 
its formation, absorbs caloric from the 
water, reduces its temperature, and actually makes 
it freeze. If the vessel of water is covered with a 
plate of metal or glass fixed to the end of a sliding 
wire, and which passes through the neck of the 
receiver, so as to be at the same time air tight and 
moveable, as shown in the above figure, the water 
will continue fluid, after the exhaustion of the 
receiver, until the cover is removed ; when in less 
than five minutes, needle shaped crystals of ice will 
shoot through it, and the whole will shortly become 
frozen. Though the water is covered with a layer 
of ice, still the evaporation and absorption of heat 
continue, for the ice itself is changed to vapour ; 
indeed, if we keep it long enough under the receiver, 
the whole of the water is frozen, and afterwards dis- 
appears, being converted to vapour, and condensed 
by the acid. In this experiment an unglazed dish 
is used for holding the water, because, being porous, 
it allows the fluid to evaporate, not only from the 
surface, but also through the sides ; hence the ice is 
first formed on the surface, and on that part in con- 
tact with the vessel. 

Another very beautiful illustration of the produc- 
tion of cold during evaporation, has been given by 
Dr WoUaston. The instrument employed is called a 
Cryophyrus^ from the Greek words kruos^ cold, and 
ferOf to bear; being a producer of cold. It is a long 



MEANS OF GENERATING COLD. 



117 



tube, forming three sides of an oblong, with a ball at 
each end. In making it, water is put into one of the 
balls, and boiled, by which the whole of the air in 
the instrument is expelled, and when in this state, 
it is sealed by a blow-pipe. When cooled, the 
vapour is condensed, and the fluid is thus under a 





diminished pressure. It must not be supposed, how- 
ever, that the pressure is entirely removed ; for 
there is still the vapour given off from the water, 
ovving to the pressure being less. If the whole of 
the water be passed into one ball, A, and the other, 
B, be surrounded by a freezing mixture, the vapour 
in it is condensed, the water in the other, is thus 
entirely relieved of pressure, and begins to pass off 
quickly in vapour, w^hich, as it flows into the oppo- 
site ball, is condensed. The vacuum is thus kept 
up, the evaporation continues, and during the forma- 
tion of the vapour, it absorbs caloric from the water, 
so as to cause it to freeze. 

The second method of generating cold, is chemi- 
cal action, chiefly when a solid is dissolved in a 
fluid, or two solids meet with each other, and be- 
come fluid. It has been already fully illustrated, 
when treating of fluidity, {see page 71.) that when a 
solid is changed to fluid it absorbs caloric. If, then, 
we can, by any means, cause a solid to become 
liquid, without the addition of heat, we diminish its 
temperature, and consequently that of any body 
brought in contact with it. 

Many of the salts, during solution in water, have 
their temperature reduced. Thus, nitre falls 17, and 
sal ammoniac no less than 5S degrees. By mixing 



118 ELEMENTS OP CHEMISTRY. 

these in equal proportions, and dissolving them, 
using five ounces of the mixture to eight of water, 
a much greater cold may be produced. That cold is 
generated is easily shewn by a thermometer, or by 
putting into the mixture a tube with water, which 
is very soon frozen. In this case, there is no waste 
of materials ; because the salts can be procured by 
evaporation, and will answer again for the same pur- 
pose. 

By dissolving a salt in an acid, by which the solu- 
tion is more quickly accomplished, the cold becomes 
more intense. Perhaps the most convenient mixture 
of this kind is Glauber's salt, and oil of vitriol, pre- 
viously diluted with its own volume of water, and 
allowed to cool. When the salt is put into this, 
using equal weights, it is quickly dissolved, and cold 
is generated. 

By the action of two solids, the product being 
fluid, the cold becomes still more intense. Thus, 
when ice is mixed with sea salt, both are liquefied ; 
and during their liquefaction, they absorb caloric, 
and of course generate cold. In this instance, the 
temperature sinks to — 4. It is the mixture always 
employed by confectioners in preparing ice creams; 
the proportions are about two of the former to one 
of the latter. There is here no waste of the salt ; 
for by boiling, the water is driven ofi", and the salt 
is procured, and will answer for the same purpose 
as before. 

This is also the mixture employed by Fahrenheit, 
in his experiments, made with a view of producing 
what he conceived to be the degree of absolute cold, 
or that at which there is no heat, and from which he 
commenced the scale of his thermometer. In this 
he committed a mistake, not only with respect to 
the temperature, for it is not 0, but — 4 ; and he 
erred also in his idea of its being absolute cold. It 
has been already stated, that lower degrees have 
been produced by other ^means. 



FREEZING MIXTURES. 115 

In using these substances for freezing mixtures, it 
must be kept in mind, that though cold is generated, 
yet, in many, heat is also given out at the same time. 
Thus, when oil of vitriol and water are mixed, there 
is a rise of temperature. Now, when the acid is 
poured on ice, the latter is liquefied, and absorbs 
heat; but the moment that water is formed, by the 
melting of the ice, it unites with the acid, and gives 
out heatj so that there is Loth the evolution and 
absorption going on. If cold be generated by this 
mixture, it is because more heat is taken in than is 
given out. Hence it is, that in dissolving Glauber's 
salt in oil of vitriol, with the view of making a 
freezing mixture, it is necessary to dilute the acid 
before putting the salt into it, to prevent it uniting 
with the water which always exists in the salt, and 
thus giving out heat. 

The instances in which we have recourse to a 
reduction of temperature, are by no means so numer- 
ous as those in which heat is applied. In warm 
climates, evaporation is often resorted to for cooling 
apartments ; for this purpose, water is sprinkled on 
branches, and leaves of plants, suspended in the 
room, during the evaporation of which, the air is 
kept agreeably cool. Ice is also procured, by the 
cold generated during this process. When the even- 
ing is calm, and the sky clear, small unglazed earthen 
dishes, with water, are placed on moistened straw 
and reeds, laid in shallow pits ; the evaporation from 
the water, and from the reeds, generates cold suffi- 
cient to form ice. It must be recollected, however, 
that in this case, a great deal of the cold is due to 
radiation ; because the sky being clear, the water 
and reeds are radiating caloric, and as there is no 
return to compensate for the loss, the temperature 
falls, {seepage 101.) We have often recourse to 
evaporation for keeping bodies cold, as in carrying 
on distillation. For this purpose, the vessel into 
which the vapour flows is covered with muslin or 



1^0 ELEMENTS OF CHEMISTRY. 

paper, and kept wet by a stream of water, which is 
constantly evaporating, and thus cooling the vapour 
w^ithin, 

TABLE OP 

Freezing Mixtures. 

Therm, sinks from 

Sal Ammoniac 5, Nitre 5, water 16, . . . 50 to 10 
Glauber's salt 3, Nitric acid + 1 water 2 . 50 to 3 
Glauber's salt 6 Sal Ammoniac 4, Nitre 2, Nitric 

acid -\~ 1 water 4 50 to 10 

Glauber's salt 8, Muriatic acid 5 .... 50 to 
Glauber's salt 5, oil of Vitriol -\- 1 water 4, . 50 to 3 

Ice 2, Sea salt 1 to- — 4 

Ice 3, oil of Vitriol + 1 water 2 .... 32 to— 23 

Ice 8, Muriatic acid 3 32 • to— 27 

Ice 4, Muriate of lime 5 32 to— 40 

For others see Manual^ p. 40. 



LIGHT. 

Light is similar to caloric in many of its proper- 
ties. They are both emitted in the form of rays, 
traverse the air in straight lines, and are subject to 
the same laws of reflection. They often accompany 
each other ; and on some occasions seem to be actu- 
ally converted into one another. It has been sup- 
posed, from this circumstance, that they might be 
modifications of the same agent; and though most 
persons regard them as independent principles, yet 
they are certainly allied in a way which is at present 
quite inexplicable. 

There are two kinds of light, natural and artifi- 
cial ; the former proceeding from the sun and stars, 
the latter from bodies which are strongly heated- 



LIGHT. 121 

The solar rays come to us either directly, as in 
the case of sunshine, or indirectly, in consequence 
of being diffused through the atmosphere, constitut- 
ing day and night. 

Light moves in straight lines with immense ve- 
locity. According to observation, it travels at a 
rate of 200,000 miles in a second, coming from the 
sun to the earth, a distance of about 6,000,000,000 
of miles in 8J minutes. Though it moves with this 
velocity, it has no sensible momentum; the most 
delicate instruments do not indicate the slightest 
impulse given by it to the objects on which it 
strikes. 

Light passes through some bodies apparently 
without obstruction, but it is absorbed by oth- 
ers ; the former are called transparent^ the latter 
opake. 

The space through w^hich light moves is called 
a 7nediuniy air and other aeriform substances, are 
termed rare, while water and transparent liquids 
and solids, are called dense media. 

When the rays of light arrive at the surface of 
bodies, apart of them, and sometimes nearly the whole, 
is thrown back, or reflected, and the more obliquely 
the light falls upon the surface, the greater in gene- 
ral is the reflected portion. In these eases the an- 
gle of reflection is always equal to the angle of inci- 
dence. 

Let a a represent pencils of light falling upon 
the surface of a polished piece of glass B, the per- 
pendicular pencil will pass on in a straiglit line to d. 
Of the oblique pencil, one portion will enter the 
glass and suffer refraction towards the perpendicular 
as at by and re-entering the atmosphere, it will bend 
from the perpendicular, and re-assume its former 
direction, as at c. Another portion of the oblique 
11 



122 ELEMENTS OF CHEMISTRY. 

pencil will be reflected at an angle equal to that of 
its incidence^ as at e. 




When any ray of light passes through an oblique 
angular crystalline body, it exhibits peculiar pheno- 
mena ; one portion is refracted in the ordinary way; 
another suffers extraordinary refraction, in a plane 
parallel to the diagonal joining the two obtuse an- 
gles of the crystal ; so that objects seen through the 
crystal appear double. Transparent rhomboids of 
carbonate of lime, ov Iceland crystal, exhibit this 
phenomenon of double refraction particularly dis- 
tinct. See Manual^ page 51. 

Sir Isaac Newton first made the discovery, that 
the rays of light coming from the sun are not sim- 
ple, but composed of different rays, possessing vari- 
ous powers of refraction, as is proved by causing 
one to pass through a triangular piece of glass called 
2i prism. For this, having darkened a room, a small 
hole is made in the shutter, and the prism, j», placed 
near it. If the ray, «, when it passes through it, 
be made to fall on a sheet of white paper, a spec- 
trura. h c, is produced, composed of seven distinct 



^mmf^mmmk 



LIGHT. 



123 



colours, red^ orange^ yellow^ greeii^ hlue^ indigo, 
violet. This separation of the rays is produced by 

C 




the difference in their refrangibility. Thus, the red 
ray is least refracted ; it is therefore least bent from 
the straight line, and is consequently lowest in the 
spectrum ; the others are situated in the order of 
their powers of refraction; the violet being most so, 
is at the top. That light is composed of these dif- 
ferent rays, is also proved by taking a quantity of 
the colours, in due proportion, and mixing them, 
by which white is produced ; or if the rays, instead 
of being thrown on paper, so as to form a spectrum, 
be made, after their separation, to pass through a 
lens, they are collected into a focus, and white light 
is produced. 

The rays of which the spectrum is composed, 
have different powers of ilkimination. Thus, if a 
small object is placed at either end, it is seen indis- 
tinctly, but if brought towards the centre, it becomes 
much more distinct. The greatest illuminating pow- 
er is between the bright yellow and the pale green. 

These rays have also different relations with res- 
pect to bodies. It has been already said, that light 
passes through transparent, but is retained by opake 
bodies. Several retain some of the prismatic rays, 
while they reflect others, and on this depend their 
appearance and colour. One which transmits all the 



124 EJLEMENTS OF CHEMISTRY. 

rays is colourless, while one which absorbs them is 
black. When a body retains all the rays but one, 
which it either transmits or reflects, it is of the col- 
our of the reflected or transmitted ray. Thus, red 
glass transmits all the rays but the red one ; blue 
cloth absorbs all but the blue one, which it reflects. 
Bodies are therefore always of the colour of the re- 
flected or transmitted ray. 

The sun's rays are the principal source, not only 
of light, but also of heat to this globe. It has been 
already mentioned, that when light strikes a polished 
body, it is reflected, or a transparent one, it is trans- 
mitted; and if the former be concave, or the latter 
convex on lioth sides, the reflected or transmitted 
rays are collected into a focus ; at this point an in- 
tense heat is excited, provided the mirror or lens 
be of sufficient size. 

The rays of which the spectrum is composed, 
possess very diSerent heating powers. When, for 
instance, the bulb of a delicate thermometer was ex- 
posed to the violet ray for 10 minutes, it rose only 
2 degrees, in the green in the same time, 3J, but in 
the red 7. It was found, however, that when the 
instrument was placed beyond the red ray, at A, it 
actually rose higher than when in it; it was affected 
even at the distance of IJ inch from the end of the 
spectrum. When placed beyond the violet ray at c, 
it was not changed. These experiments prove, that 
solar light is composed not only of a luminous, but 
also of a heating ray, and which has been found to 
be quite distinct from the former, possessing laws 
peculiar to itself; thus, they are less refrangible, 
hence they are placed beneath them in the spectrum. 
They can be reflected or transmitted, and collected 
into a focus, like the others, and hence the source of 
the heat produced by a lens, when the solar rays are 
allowed to pass through it, or by a metallic concave 
mirror, when they are reflected and concentrated. 
It has been mentioned, that the .different coloured 



CHEMICAL EFFECTS OF LIGHT. 125 

rays of the spectrum have different heating powers; 
this, it has been found, depends on an admixture of 
the heating rays. Thus, the red, which is nearest 
the latter, has the greatest, and the violet, which is 
at the greater distance, has the least effect on a ther- 
mometer ; the effect gradually diminishing, as we 
proceed from one end to the other. 

Light possesses considerable influence over the 
chemical energies of bodies. If a mixture of equal 
volumes of the gases called chlorine and hydrogen 
be exposed in a dark room, they slowly combine, 
and produce muriatic acid gas ; but, if exposed to 
the direct rays of the sun, the combination is very 
rapid, and often accompanied by an explosion. 

Chlorine and carbonic oxide have scarcely any ten- 
dency to combine, even at the highest temperatures, 
when light is excluded, but exposed to the solar rays 
they enter into chemical union. Chlorine has little 
action upon water, unless exposed to light ; and, 
in that case, the water, which consists of oxygen 
and h57drogen, is decomposed. The hydrogen unites 
with the chlorine to produce muriatic acid, and the 
oxygen is evolved in a gaseous form. 

A familiar instance of the effect of light in produ- 
cing chemical changes, is the blackening of indelible 
or marking ink, the traces of which are at first invi- 
sible, but soon become black ori exposure to sun-shine, 
or even to day-light. The prismatic rays have dif- 
ferent powers in inducing these changes. When, 
for instance, a spectrum is produced, and a line is 
drav^n with the ink, in the different rays, and ex- 
posed to sun-shine, that in the violet ray is soonest 
blackened. 

The discovery of a heating ray beyond the lumi- 
nous ones in the spectrum, naturally suggested the 
idea of the chemical effects being produced in a sim- 
ilar manner. On placing the traces with the marking 
ink above the violet ray, c, it has been found not 
only to be blackened, but to become so, much sooner; 
11* 



126 ELEMENTS OF CHEMISTRY. 

from which it is concladed, that, besides rays of heat 
and Jight^, there is also one acting chemically, and 
which is quite distinct from the others, and govern- 
ed by its own laws. It has been found, that the 
blackening produced by holding the traces in the 
different raj^s, was occasioned totally by the admix- 
ture of this with the luminous rays. 

Suoh is the idea in general entertained concerning 
the constitution of solar light, — that it is composed 
of three distinct rays, each having its own proper- 
ties, — the light-giving or luminous ; the heat-caus- 
ing, or calorific ; and the chemical-acting ray ; which 
may be separated entirely from each other. 

The influence of light over the objects of nature 
is very great. By its rays entering the eye, vision 
is produced. The effects on the vegetable world 
are not less striking. Plants always extend their 
branches to the light, and many of them follow the 
course of the sun. When completely excluded from 
its influence, they become feeble, insipid, and colour- 
less ; but, when again exposed to it, they regain 
their strength, and assume their former appearance. 
On this depends the operation of blanching^ which 
is merely excluding the plant, suppose celery, from 
light, by covering it with earth, by which its colour 
is banished, and its flavour altered. The effects of 
light on inanimate objects are numerous. One of 
these has been mentioned,~the blackening of mark- 
ing ink, which is owing to the decomposition of the 
salt of silver which it contains ; changes of a similar 
nature are produced on other bodies, which will be 
afterwards mentioned. 

The more refrangible rays of light possess the 
property of rendering steel or iron magnetic. This 
property was discovered in the violet ray, by Dr 
Morrichini, and has been since established by Mrs 
Somerville, who recently gave an account of her re- 
searches to the Royal Society. Sewing needles 
were rendered magnetic by exposure for two hours 



SOLAR PHOSPHORI. 127 

to the violet ray, and the magnetic property was com- 
municated in a still shorter time^ when the violet 
rays were concentrated by a lens. The indigo rays 
possess the magnetizing power almost to the same 
extent as the violet ; and the blue and green possess 
the same power, though in a less degree. It is want- 
ing in the yellow, orange and red. Needles were 
also rendered magnetic by the sun's rays, transmit- 
ted through green and blue glass. 

There are many substances, which, when heated 
to a certain point, become luminous without under- 
going combustion, and such bodies are said to be 
phosphorescent. Some varieties of phosphate of 
lime, of fluor spar, of marble, and certain salts are 
the most remarkable bodies of this description. 
Their luminous property may be best exhibited by 
scattering them in coarse powder upon an iron plate 
heated nearly to redness. 

Another class of phosphorescent bodies have been 
termed Solar phosphori, from becoming luminous 
when removed into a dark room, after having been 
exposed to the sunshine. Of this description are 
Canton's, Baldwin's, and the Bolognian phosphorus. 
The first is prepared thus ; — Calcine oyster shells in 
the open fire for half an hour, then select the whitest 
and largest pieces and mix them with one third their 
weight of flowers of sulphur, pack the mixture close- 
ly into a covered crucible, and heat it to redness 
for an hour, when the whole has cooled select the 
whitest pieces for use.* 

A third set of bodies are spontaneously phospho- 
rescent^ such as the flesh of salt water fishes just be- 
fore it putrefies, and decayed wood. 

Percussion and friction are often attended by the 
evolution of light, as when flint pebbles, pieces of 
sugar, &c. are struck or rubbed together. 

* See Manual, p. 56. 



128 



ELEMENTS OF CHEMISTRY. 



PARTICULAR DOCTRINES. 

In the preceding chapters, the general doctrines of 
chemistry, heat, light, and chemical attraction, have 
been treated of, — electricity and galvanism will be 
considered afterwards. We now proceed to the 
more particular ones, which consist of a detail of 
the chemical properties of different bodies. In this 
part of the subject, our remarks will be confined to 
those substances which are used in the arts, and for 
domestic purposes, and to such as have some influ- 
ence in the various operations carried on by practi- 
cal chemists. First of the 

AIR OF THE ATMOSPHERE. 



Atmospheric Air, or that mass of aerial fluid 
which surrounds the globe, possesses, like all other 
aeriform bodies, compressibility and elasticity. By 
compressibility is meant, that the particles may be 
brought nearer each other, or that it may be made 
to occupy less space than it naturally does. Thus, 
if it be subjected to pressure, it is diminished, as is 
shewn by taking a bent tube, shut at «, 
and open at b. By pouring in a little ^. 
mercury, so as to occupy the bent part at 
c, air is confined in the shorter limb, 
and we can subject this to pressure by 
putting in more mercury, say to d^hy d' 
which that in the opposite limb rises, 
' say to e, shewing that the air is reduced 
in volume. If it be poured in to f, it 
will rise in the other, say to g, proving 
that the air is still farther diminished. 
It has been proved by experiment, that 
the diminution is in proportion to the pressure. 
That is, if twice the pressure which it usually sus- 





ATMOSPHERIC AIR. 129 

tains be applied, it is reduced to one-half, if four 
times the pressure to one-fourth, and so on. It is 
remarkable, that during the condensation of air, heat 
is disengaged, sufficient to set fire to inflammables, 
(see page 107.) 

As the pressure is removed, the air regains its 
former size, or if part of that which it always sus- 
tains is withdrawn, it enlarges ; hence it is said to 
have elasticity. The elasticity of the air is shewn 
^ by placing a bladder half full of it, 
a, under the receiver of an air-pump, 
6, and exhausting; as we withdraw 
the air, in other words, diminish the 
pressure, the bladder becomes dis- 
tended, c, from the enlargement of 
the air within it ; indeed, the whole 
operation of the pump itself depends 
on the elasticity of the air ; for when the piston,/*, 
{see cut^page 76), is drawn up, by which a vacuum 
is produced in e, the air in the receiver, a^ owing 
to its elasticity, expands, and part of it rushes into 
the syringe. When the piston is forced down, this 
air is expelled through the valve, h) and on again 
raising it, more is drawn out, so that, by alternately 
raising and depressing the piston, almost the whole 
may be withdrawn. It is evident, however, that the 
whole cannot be taken out ; for when the elasticity 
of what remains in becomes trifling, it ceases to 
move the valve, so that any farther working of the 
pump does not withdraw more air. The more easily 
therefore, the valves are moved, the more nearly does 
the vacuum approach to a perfect one. 

Experiments have shewn, that the enlargement 
keeps pace w4th the diminution of pressure ; that is, 
if one-half of the original pressure be removed, it 
is doubled in its volume, and so on. 

Air is also possessed of weight ; but this diflers 
according to the height of the place at which it is 
taken. As that below sustains all aboye it, it is 



130 



ELEMENTS OF CHEMISTRY. 



A 



a 



much compressed, and is therefore the heaviest. 
The weight of the air, in other words, the pres- 
sure of the atmosphere^ is proved in many ways. 
If a receiver be placed on the plate of an air-pump, 
and exhausted, we are unable to move it, because it 
is kept down by the weight of the air around it. If, 
instead of using the receiver for this experiment, a 
tin cylindrical box, be employed, as the air within 
is withdrawn, the sides are driven in, not being able 
to sustain the weight of the air around it. Or if a 
long tube, «, with a stop- a 
cock, be exhausted by the 
pump, and then have the 
cock opened under water, 
i, the fluid will be forced 
in by the pressure of the air 
on the surface of that in the 
basin. It has been ascer- 
tained by experiment, that 
the pressure of the air is, on 
an average, equal to 15 lb. 
on the square inch, which is 
the same as that of a column 
of mercury of 30 inches. 
If, therefore, a long tube, 
a, shut at one end, be filled 
with mercury, and inverted 
in a cup of the same fluid, 
only part of that in the tube 
escapes, there will remain about 30 inches, c, retain- 
ed there by the pressure of the air on the surface of 
that in the cup. Were the pressure increased, the 
mercury would stand higher ; were it, on the con- 
trary, diminished, it would be lower. This has 
given rise to the use of a tube containing mercury, 
and inverted in a basin of it. as a measure of the 
pressure of the atmosphere; and as the air varies in 
weight, according to its state with respect to dry- 
ness and moisture, we have thus an indication of any 




e 



ATMOSPHERIC AIR. 131 

change likely to take place in the weather. The 
instrument is called a barometer, from the Greek 
words barus, signifying heavy, and metron, a 
measure. If the mouth of the tube, in the former 
experiment, be plunged under water, the mercury 
will escape, and the water will rise; but, in this case, 
it will fill the tube, because water being a lighter 
fluid than mercury, the air can sustain a greater 
column of it It has been found, that the pressure 
of the air is equivalent to that of a column of water, 
of about 34 feet ; if the tube, then, were of this 
length, the water would fill it, being forced in by 
the pressure of the air. Hence it is that we are 
enabled to raise water only to a certain height in a 
pump ; for when the piston is drawn up, a vacuum 
is produced, which is immediately filled by the fluid 
at the bottom being forced in by the air pressing 
on it^ but when this is brought up to about 34 feet, 
any farther working of the pum.p does not elevate 
the water more, because, though a vacuum be pro- 
duced, the pressure of the air cannot sustain a longer 
column 

The full illustration of this important subject be- 
longs to Mechanical Philosoph}^ ; the few remarks 
made, will suffice to point out its agency in chemi- 
cal processes. 

The chemical qualities of air are numerous, and 
it serves important purposes in the economy of 
nature. Two of these may at present be noticed ; 
the others will be detailed in giving the properties 
of the substances with which it acts. 

Air does not suffer any particular change by the 
addition of heat, except an enlargement ; and that 
it is enlarged, is shewn by heating slightly a flaccid, 
but air-tight bladder, which very soon becomes 
quite tense. Different statements have been given 
of the enlargement produced in air by each addition 
of certain quantities of caloric. According to onCj in 
rising from 32 to 50, it was found to enlarge 4^0^^ 



13^ ELEMENTS OP CHEMISTRY* 

part, for each degree added. Others, on the con- 
trary, say, that it is 4^9th part, while others make 
it 4|^th. From the most accurate experiments 
lately performed, the enlargement has been fixed 
at 4loth part for each degree, commencing at 32 ; 
and it has been found also, that the increase in 
volume is the same, whether the air be under the 
usual, or an increased pressure, provided the addi- 
tional pressure is kept up. The preceding remarks 
apply not only to air, but to all other aeriform fluids, 
the expansion being the same in all, j^o^h part for 
each degree. Since air is so much enlarged by heat, 
it is necessary to pay particular attention to the 
temperature. Hence it is, that 60 has been gen- 
erally fixed on as a standard. Should we not be 
able to experiment on it at this, allowance must 
be made, according to the difference. — See Appen- 
dix. 

Air is essential for the life of the higher classes 
of animals ; for if any of them be confined in the 
exhausted receiver of a pump, it speedily dies. A 
renewal of it is also necessary ; for, if an animal be 
kept in a confined quantity, life is also soon ex- 
tinguished, because its properties are completely 
altered, by which it is no longer able to support re- 
spiration. That its qualities are changed, is shewn 
by filling a vessel with air from the lungs, and put- 
ting into it a lighted candle, which is instantly ex- 
tinguished. This shews the necessity of ventilating 
crowded apartments, that the air which has been 
breathed may b^ removed, and another portion sup- 
plied. 

Air is also necessary for combustion. A candle 
will not burn in an exhausted vessel ; the flame is 
even extinguished, unless the air be renewed. 

Exp. 57 — Thus if a candle be put into a jar of air, standing 
over water, the combustion continues but for a short time. If a 
lighted taper be put into what remains, it is also extinguished, 
shewing that the properties are changed. 



NOMENCLATURE. 133 

These experiments prove the necessity of air, both 
for respiration and combustion. It is not, however, 
a simple body ; it is composed of two ingredients, 
which can be easily separated, and by particular 
means may be obtained in their pure state. 

They are both transparent, colourless gases, and 
cannot therefore be distinguished by the eye ; but 
they are easily known by their properties. The 
one is called oxygen^ the other nitrogen^ or azote ; 
the former so called from the Greek words oxus^ 
signifying acid^ and ginomai^ to generate, because, 
by its union with some bodies, it generates acids ; 
the latter has its name derived from nitre, and the 
Greek word to generate, because, by entering into 
combination with others, it generates nitre and nitric 
acid. The term azote is derived from the Greek 
word zoe, signifying life,* 

In giving an account of these and other gaseous 
bodies it will be necessary to make use of the pecu- 
liar language of Chemistry. 

NOMENCLATUKE. 

The following examples may serve to give some 
idea of the principles upon which the nomenclature 
of chemistry is constructed. 

When any body unites with oxygen, whatever 
the product may be, the process is termed oxygena- 
tion. When only a certain portion of oxygen com- 
bines with other bodies, the product not acquiring 
acid properties, the process is termed oxidation, 
and the new compounds are usually distinguished by 
the termination ide, — as oxide of chlorine, oxide of 
nitrogen. In like manner similar combinations of 
chlorine and iodine are distinguished as chlorides, 

* In the Greek language, the letter a is used in the same way as in, ?m, &c. in 
English. Thus, secure, insecure, like, unlike. In Greek, zoe, signifies life ; but 
with the addition of a, witliout life. Hence, azote is so called, because it is 
destructive of life. 

12 



134 ELEMENTS OF CHEMISTRY. 

and iodides — thus we have chloride of sulphur^ 
iodide of iron, &c. 

When more than one compound of this kind is 
produced, the terminations ous and ic are used to 
designate the relative proportions of the electro- 
negative substances. Thus nitrogen forms two ox- 
ides ; that containing the smallest proportion of 
oxygen is the nitrous oxide, that containing the 
largest the nitric oxide. The acid compounds are 
similarly designated, as nitrous and nitric acid; 
sulphurous and sulphuric acid ; and w^here there 
are intermediate compounds the term hypo is occa- 
sionally added to the acid next above it in point of 
oxidizement. Thus, hyposulphuric acid signifies an 
acid compound intermediate between sulphurous and 
sulphuric acids ; hypophosphorous acid, an acid con- 
taining less oxygen than the phosphorus acid-. 

The different combinations of the metals with oxy- 
gen, are best distinguished by prefixing to the word 
oxide the first syllable of the Greek ordinal nume- 
rals. Thus the protoxide of a metal will denote 
the compound containing a minimun of oxygen, or 
the first oxide which the metal is capable of forming; 
deutoxide will denote the second oxide of a metal, 
&c. ; and when a metal is combined with the largest 
possible quantity of oxygen, the compound, if not 
acid, may be called/?^ro^zrfe. The same rule applies 
to the chlorides and iodides. 

The acids terminating in ous produce compounds 
in which the termination ite is used ; while those 
ending in ic form compounds in which the ending 
ate is used. Thus the combination of sulphurous 
acid and potassa, is a sulphite of potassa ; that of 
sulphuric acid and potassa, a sulphate of potassa, 
&c. 

When the same acid combines with more than 
one oxide of the same metal, the first syllable of the 
Greek ordinal numeral is in that case applied to the 
acid ; thus, the protosulphate and persulphate of 



APPARATUS. 135 

iron signify the combinations of sulphuric acid with 
the protoxide and peroxide of iron. 

The compounds of the simple inflammable bodies 
with each other and with the metals are commonly- 
designated by the termination uret^ as sulphuret 
of phosphorus, phosphuret of carbon, carburet of 
iron, &c. 

The terms bi-sulphuret , hi-sulphate^ bi-phosphii- 
ret J bi'phosphate^ &c. applied to compounds, imply 
that they contain twice the quantity of sulphur, sul- 
phuric acid, phosphorus or phosphoric acid, existing 
in the respective sulphuret, sulphate, phosphuret and 
phosphate. 

The term gas is applied to all permanently elastic 
fluids, except the atmosphere, to which the term air 
is appropriated. 

For performing the necessary experiments on 
gases, a few articles of apparatus are necessary, con- 
sisting partly of vessels fitted for containing the ma- 
terials thatafibrd them, and partly of vessels adapted 
for the reception of gases^ and for submitting them 
to experiment. 

For procuring such gases as are producible w^ith- 

out a very strong heat, glass bottles, furnished with 

j^^ ground stoppers and bent tubes, are 

%^^ n sufficient. Of these, several will be 

/\ required of diflerent sizes and shapes, 

I adapted to diflerent purposes. If these 

*^ — J cannot be procured, a Florence flask, 

with a cork perforated by a bent glass tube, or even 

by a tin pipe, will serve for obtaining some of the 

gases. 

Those gases, that require, for their liberation, a 
red heat, may be procured by exposing to heat the 
substances capable of affording them, in coated 
earthen retorts or tubes ; or, in a gun barrel, the 
touch-hole of which has been accurately closed by an 



136 



ELEMENTS OF CHEMISTRY. 



iron pin. To the mouth of the barrel must be affixed 
a glass tube, bent so as to convey the gases where 
they m.ay be requisite. 

For receiving the gases, glass jars, of 
various sizes, are required, some of which 
should be furnished with necks at the 
top, fitted with ground stoppers. Others 



should be provided with brass caps, and 



screws, for the reception of air 
cocks. Of these last, (the air-cocks) 
several will be found necessary ; 
and to some of them bladders, or 



A 




elastic bottles, should be firmly tied, 
for the purpose of transferring gases. These jars 
will also be found extremely useful in experiments 
on the properties and effects of the gases. Some of 
them should be graduated into cubical inches. 

To contain these jars 
when in use, a vessel 
will be necessary, capa- 
ble of holding a few gal- 
lons of water. This may 
either be of wood, if of 
considerable size ; or, if 
small, of tin, japanned or 
painted.* 




*F'F, "exhibits a 
section of this.appa-, 
latus, which has been 
termed the pneumcftQ- 
chemical trough, or 
pneumatic cistern. Its 
size may vary with that 
of the jars employed ; 
and, about two or three 
inches from the top, it 
should have a shelf, 6, on 
which the jars may be 
placed, when filled with 
air, without the risk of 
being overset. In this 
shelf should be a few 
small holes, to which 
inverted funnels may be 
eeldered. 




GAZOMETER. 



137 



A glass tube, about IS inches long, and three 
quarters of an inch diameter, closed at one end, 
and divided into cubic inches and tenths of inches, 
will be required for ascertaining the purity of 
air by nitrous gas. It should be accompanied 
also with a small measure, containing about two 
cubic inches, and similarly graduated. 



An apparatus, almost indispensable in experiments 
on this class of bodies, is a Gazometer^ which ena- 
bles the chemist to collect and to preserve large 
quantities of gas, with the aid of a few pounds of 
water. It consists of an outer 
fixed vessel, d, and an inner move- 
able one, c, both of japanned iron. 
The latter slides easily up and down 
X. within the other, and is suspend- 
ed by cords passing over pulleys, 
to which are attached the counter- 
poise, e e. To avoid the incum- 
brance of a great weight of water^ 
the out^er vessel, d, is made double, 
or is composed of two cylinders, 
the inner one of which is closed 
at the top and at the bottom. The 
space of only about half an inch is 
the two cylinders, as shown by the 
dotted lines. In this space, the vessel, c, may move 
freely up and down. The interval is filled with 
water as high as the top of the inner cylinder. The 
cup, or rim, at the top of the outer vessel, is to pre- 
vent the water from overflowing, when the vessel, c, 
is forcibly pressed down, in which situation it is 
placed, w^henever gas is about to be collected. The 
gas enters from the vessel in which^it is produced, 
by the communicating pipe, 6, and passes along the 
perpendicular pipe, marked by dotted lines in the 
centre, into the cavity of the vessel^ c, which con- 
tinues rising till it is fulL 
12"^ 




left between 



138 



ELEMENTS OF CHEMISTRY. 



To transfer the gas or to apply it to any purpose^ 
the cockj J, is to be shut, and an empty bladder, or 
bottle of elastic gum, furnished with a stop cock, to 
be screwed on a. When the vessel, c, is pressed 
down with the hand, the gas passes down the cen- 
tral pipe, which it had before ascended, and its escape 
at b being prevented, it finds its way up a pipe w^hich 
is fixed to the outer surface of the vessel, and w^hich 
is terminated by the cock, a. When it is required 
to transfer the gas into glass jars standing inverted 
in w^ater, a crooked tube may be employed, one end 
of which is screwed upon the cock, b ; while the 
other aperture is brought under the inverted funnel, 
fixed into the shelf of the pneumatic trough.* 

•* When large quantities of gas are required, the gas-holder, 
will be found extremely useful. It is made of tinned iron-plate, 
japanned both within and without. Two short pipes, a and c, 
terminated by cocks, proceed from its sides, and another, 6, passes 
through the middle of the top or cover, to which it is soldered, 
and reaches within half an inch of the bottom. It will be found 
convenient also to have an air-cock with a very wide bore, fixed 
to the funnel at h. When gas is to be transferred into this vessel 
from the gazometer, the vessel is first completely filled with wa- 
ter through the funnel, the cock, a, being left open, and c shut. 
By means of a horizontal pipe, the aperture a is connected with 
a of the gazometer. The cock, 6, being shut, a and c are open, 
and the vessel, c, of the gazometer, gently pressed downwards 
with the hand. The gas then descends from the gazometer tiU 
the air-holder is full, which may be known by the water ceasing 
to escape through the cock, c. All the cocks are then to be shut^ 

und the vessel disunited. To apply this gas to 

any purpose, an empty bladder may be screwed 

on a ; and water being poured through the fun- 

ifiel, 6, a corresponding quantity of gas is forced 

into the bladder. By lengthening the pipe, fc, 

the pressure of a column of water may be add- 
ed : and the gas, being forced through a with 

"■onsiderable velocity, may be applied to the 

purpose of a blow-pipe, &.c. The apparatus 

admits of a variety of modifications. The 

most useful one appears to be that contrived by 

Mr. Pepys, consisting chiefly in the addition of a 

shallow cistern to the top of the air-holder, 

and of a glass register tube, /, which shows the 

height of the water, and consequently the quan- 
tity of gas, in the vessel. When a jar is intend- 
ed to be filled with gas from the reservoir, it is 

placed, filled with water, and inverted, in the 

cistern, c. The cocks 1, and 2, being opened, the 

water descends through the pipe attached to the 

tatter, and the gas rises through the cock, e. By 

iai«ing the cistern .o.to a greater elevation, any 

degree of pressure rr.ay be obtained ; and a 

lt!ov/-pipe, d^ may be screwed on the cock at the 

'ii?f t 9i4e of the vfi^seL 





OXYGEN. 139 

The gazometer already described, is fitted only 
for the reception of gases that are confinable by 
water ; but for those which are absorbed by water it 
is necessary to make use of quicksilver; for the 
description of an apparatus for this purpose, see Man- 
iial^p, 70. 

For the mere exhibition of a few experiments 
on these condensible gases, a small trough, eleven 
inches long, two wide, and two deep, cut out of a 
solid block of mahogany, (or soap-stone) is sufficient 
Previously to undertaking experiments on the 
gases, it may be well for an unpracti&ed experimen- 
talist to accustom himself to the dexterous manage- 
ment of gases, by transferring common air from one 
vessel to another of different sizes.* 

The process of weighing a gas is to ex- 
haust a light globe or flask, 6, fitted with a cap 
and stop cock for the purpose, then exactly 
to counterpoise it, to attach it to a graduated 
jar, «, containing the gas to be weighed, and 
after allowing as much as will enter to pass 
in, permitting the temperature to become 
that of the atmosphere and equalizing the 
pressure without the jar, to estimate the vol- 
ume that has entered, by the graduation. 
Then on weighing the vessel, it may be ascer- 
tained how much it has increased in weight, 
and the increase will of course be the weight 
of the observed volume of gas.t 

OXYGEN. 

Oxygen has never been obtained in a state of com- 
plete separation. In the state of gas, it is combined 
v/ith caloric, and probably with light and electricity. 
It was discovered in 1774 by Dr Priestly who gave 
it the name of dephlogisticated air. 

This gas may be obtained from various sub- 
stances ; but most economically from the black oxide 

* See Manual, p. 8a t Ibid, p. 81. 




140 ELEMENTS OP CHEMISTRT. 

of manganese, heated to redness in a gun-barrel, or 
in an iron retort : or from the same oxide, heated bj 
a lamp in a retort, or gas bottle, with half its weight 
of strong sulphuric acid. One pound of manganese 
is capable of furnishing from 40 to 50 wine pints 
of gas. 

It may be also obtained from nitrate of potassa, 
(common saltpetre) made red-hot in a gun-barrel, or 
in a coated earthen retort; and from chlorate of 
potassa heated in a small glass retort, over an Ar- 
gand's lamp. The oxygen gas thus produced is 
much purer than that obtained in any other mode. 

All these substances, after having yielded oxygen 
gas, are found considerably diminished in weight; 
and calculating each cubic inch of gas to be equal to 
one-third of a grain, the loss of weight will be found 
pretty exactly equivalent to that of gas generated. 

Oxygen gas is insipid, colourless and inodorous. 
It is so sparingly absorbed by water, that when 
agitated in contact with it, no perceptible diminution 
takes place. It is rather heavier than common air. 

It is a powerful supporter of respiration and com- 
bustion. A small animal, confined in oxygen gas, 
lives thrice as long as when confined in the sam^ 
bulk of common air. — This effect seems connected 
with the absorption of oxygen by the blood. 

Exp. 58. — Pass up a little dark-coloured blood into a jar partly 
filled with oxygen gas, and standing over mercury. The gas will 
be in part absorbed, and the colour of the blood will be changed 
to a bright and florid red. This change to red may be shown, by 
putting a little blood into a common vial filled with oxygen gas 
and shaking it up. 

All combustible bodies burn in oxygen gas with 
greatly increased splendour. 

Exp. 59.— a lighted wax taper, fixed to an iron wire, and plung- 
ed into a vessel of this gas, burns with great brilliancy. If the 
taper be blown out, and Jet down into a vessel of the gas while 
the snufi" remains red-hot, it instantly rekindleF, with a slight ex- 
plosion. 



OXYGEN. 



141 



A red-hot bit of charcoal, fastened to a copper wire, 
and immersed in the gas, throws out beautiful sparks. 

Exp, 60. — Let a small piece of phosphorus be placed 
in a hemispherical tin cup, which may be raised by 
means of the wire stand, two or three inches above 
the surface of water contained in a broad shallow dish. 
^^^ Fill a bell-shaped receiver, having an open neck at the 
^^^:=:^ top to which a stopper is ground, with oxygen gas ; 
and, as it stands inverted in water, press a circular piece of paste- 
board, rather exceeding the jar in diameter, over its mouth. 
Cover the phosphorus instantly with the jar of oxygen gas, re- 
taining the pasteboard in its place, till the jar is immediately over 
the cup. When this has been skilfully managed, a very small 
portion only of the gas will escape. The stopper may now be 
removed, when the water will rise to the same level within as 
without the jar, and the phosphorus may be kindled by a heated 
copper wire. 

Exp. 61. — Substitute for the phosphorus a small ball formed of 
turnings of zinc, in which about a grain of phosphorus is to be 
enclosed. Set fire to the phosphorus as before. The zinc will 
be inflamed, and will burn with a beautiful white light. A simi- 
lar experiment may be made with metallic arsenic, which may 
be moistened with spirit of turpentine. The filings of various 
metals may also be inflamed, by placing them in a small cavity, 
formed in a piece of charcoal, igniting the charcoal, and blowing 
on the part containing the metal, a stream of oxygen gas from a 
bladder, or the gas-holder, see note, page 138. 

Exp. 62. — Procure some thin harpsichord wire, and twist 'At 
round a slender rod of iron or glass, so as to coil it up in a spiral 
form. Then withdraw the rod, and tie a little thread or flax round 
one end of the wire, for about one 20th of an inch ; which end 
is to be dipped into melted sulphur. The other end of the wire 
is to be fixed into a cork; so that the spiral 
may hang vertically. Fill, also, with oxygen 
gas, a bottle capable of holding about a 
quart, and set it with its mouth upwards. 
Then light the sulphur and introduce the wire 
into the bottle of gas, suspending it by the 
cork The iron will burn with a most brilliant 
light, throwing out a number of sparks, which 
fall to (he bottom of the bottle, and generally 
break it. This accident, however, may fre- 
quently be prevented by pouring sand into the 
bottle, so as to lie about half an inch deep on 
the bottom ; or by using an air jar in a dish 
containing water. 

During every combustion in oxygen gas, the gas 
suffers a considerable diminution. To exhibit this, 




142 ELEMENTS OP CHEMISTRY. 

experimentally, in a manner perfectly free from all 
sources of error, would require such an apparatus as 
few beside adepts in chemistry are likely to pos- 
sess.* 

It has been formerly remarked, that by the speedy 
renewal of air to a burning body, the combustion 
becomes more rapid, and the heat more intense. 
This, the preceding remarks shew, is merely by 
supplying that part absolutely necessary for combus- 
tion, by which the inflammable matter is rapidly 
consumed. 

NITROGEN. 

Nitrogen gas is always obtained by the decompo- 
sition of air, which, it has been already said, is a 
compound of it and oyxgen. For this purpose, we 
have merely to deprive it of its oxygen, and nitro- 
gen is left. The substance commonly employed for 
this purpose, is a mixture of 1 of flowers of sulphur, 
and 3 of iron filings moistened. It is 
put into a dish, «, over which a bell jar, 
b, is placed, resting below in a basin of 
water, c. On leaving it there for some 
hours, the oxygen of the air in the jar 
unites with the sulphur and iron, and 
, the water rises to supply its place, say 



to d. What is left is nitrogen; and 
that it is so, is proved by putting into 
it a lighted candle, which is instantly extinguished. 
If we wish to expel the gas from 5, we have merely 
to adapt a tube to the stop-cock, e, and pour in water 
to c, which, when the stop-cock is opened, forces 
out the gas; s(5 that, by putting the tube under a jar 
in a water-trough, it may be collected. 

Nitrogen ma3r also be procured from the lean part 
of flesh meat, which may be put into a gas bottle, 
along with very dilute nitric acid. By a heat of 
about 100^ the gas is disengaged and may be collect' 

* See Manual, p. 86. 





INFLAMMATION, OR COMBUSTION. 143 

ed over water. It is derived from the animal sub- 
stance, not from the acid. 

That the properties of oxygen and nitrogen gases 
are different, is shewn by putting a lighted taper 
-^ into nitrogen, N, by which it is 
instantly extinguished; but when 
removed from it, and put into 
oxygen gas, 0, provided there is 
a little of the wick still red, it is 
rekindled, and burns with much 
greater splendour than in air. 
If four measures of nitrogen be mixed with one of 
oxygen and a candlje be put into the mixture, it will 
burn in it as in air. 

HYDROaEN, INFLAMMABLE AIR, OR FIRE DAMP. 

Before proceeding to treat of hydrogen, as it and 
some of the substances which follow it are inflamma- 
ble, it is necessary to premise a few remarks on 

Inflammation or Combustion. 

By combustion is meant, that some bodies, when 
heated to a certain state, have their temperature 
instantly raised above the surrounding medium, and 
emit light more or less copiously. In many cases 
they seem to be consumed ; in most, at least, the 
products are not apparent. The substances that 
undergo this change, are called inflammables or 
combustibles. A combustible is easily distinguish- 
ed from an incombustible. When heat is added to 
the latter, it arrives at the temperature of the sur- 
rounding medium ; but the moment that we cease 
to apply it, its temperature falls. When, on the 
contrary, the former is heated to a certain height, it 
gives forth heat and light, and continues to do so for 
some time, though the means by w^hich its tempera- 
ture was raised is withdrawn. 

It has been said, that some inflammables appear 
to be annihilated during combustion. Thus, when 



144 ELEMENTS OP CHEMISTRY. 

strong spirit of wine is kindled, in a saucer, the 
whole of it disappears. But, in this case, it is not 
annihilated; it is merely changed into other substan- 
ces, but which we do not observe, as they are in the 
gaseous form, 

Exp. 63. — That the substance is not annihi- 
lated during combustion, is shewn by setting fire 
to a piece of phosphorus, a, and putting a bell 
glass over it, fe. A white flaky matter is formed, 
and deposited on the sides of the apparatus. --— — ^ — ^-^ 

The same is the case in every instance; the inflam- 
mable being merely converted into another body. 

To keep up combustion, air, or some body that 
will supply oxygen, is necessary.* It has been 
already remarked, {see page 132), that a candle will 
not burn in an exhausted vessel; even when kept in 
a confined quantity of air, it is soon extinguished. 
Air, also, in which a candle has been burned, is 
reduced in volume, and its properties are completely 
changed. To shew that this is the case, some con- 
trivance must be resorted to, to prevent its escape 
when heated. 

Exp. 64. — If sulphur or phosphorus, a, be kindled, \ ^ / 
and a jar open above and below, 6, but having a \ / 

tube with a bladder fitted to the upper aperture, c, yf^ 

be placed over it, the air below being confind by /fil \ 
water, dj the combustion continues but for a shoit 
time; and after it has ceased, and the apparatus 
become cold, the water rises in the jar, e, shewing 
that part of the air has been consumed. If a taper 
be put through the upper aperture, into the residual i 
gas, it is extinguished. M^ t~~B' — :^ 1 

The diminqtion, therefore, is owing to the abstrac- 
tion of oxygen ; the nitrogen is left. Combustion 
must therefore be considered as the union of an 
inflammable with the oxygen of the atmosphere; 
hence the necessity of a renewal of it, for keeping 
up this process. 

* These remadcs apply to common instaiwes of combustion. 



HYDROGEN. 145 

After these preliminary observations, we now 
proceed to the properties of 

HYDROGEN. 

Hydrogen is a transparent and colourless aeriform 
substance ; of course, it cannot in appearance be 
distinguished from atmospheric air. It has in gene- 
ral a disagreeable odour, but derived from the impu- 
rities of the bodies by which it is prepared ; for when 
pure, it is free from smell. It is the lightest gas, 
consequently the lightest object, with which we are 
acquainted. When pure, it is at least fourteen times 
lighter than atmospheric air ; or, taking the specific 
gravity of the latter as 1000, that of the former is 
only 69 ; of course, when it escapes from a vessel 
into the atmosphere, it always ascends. 

The most remarkable property of hydrogen, is its 
inflammability. When a lighted taper is applied to 
it, it is kindled, and burns with a reddish flame; but 
the rapidity of the combustion depends on the man- 
ner in which the jar containing it is held. If the 
mouth be kept down, it burns slowly; because, being 
much lighter than air, it is kept in the jar, and as it 
burns only where it is in contact with the atmos- 
phere, the combustion is slow. When on the con- 
trary, the mouth is held up, it is quickly consumed, 
because it rises, and mixes with the atmosphere. In 
these experiments, the hydrogen enters into union 
with the oxygen of the air. If, instead of setting 
fire to the hydrogen in air, it be mixed with oxygen, 
and heat applied to the mixture, it 
explodes with great violence. This 
may be easily done, by mixing them in 
o a strong glass phial, in the proportion 

t> I of two of hydrogen, A, A, to one of 

— -^ oxygen, o, and applying flame to the 
mouth of the vessel. In this instance, also, the 
gases combine, and, by their union, form a new 
substance, which is water. 
13 



[ 



146 



ELEMENTS OF CHEMISTRY. 




That hydrogen, by its combustion, forms water, 
is easily shewn. We have merely to set fire to a 
stream of gas, coming by a 
pipe, «, from a gas-holder, 
and allow it to burn in a 
globular vessel, b^ with a 
very small flame, the glass 
will very soon become dim, 
from the decomposition of moisture. If the com- 
bustion be carried on suj9Sciently long, globules of a 
transparent colourless fluid trickle down the sides. 
In this instance, the hydrogen unites with the oxygen 
of the atmosphere, water being the product of the 
action. . 

To render the proofs of the composition of this 
fluid still more satisfactory, it can be shewn that it 
contains oxygen and hydrogen. If water be allowed 
to fall, drop by drop, into a red hot iron tube, or if 
it be passed in the state of steam through it, it is 
instantly decomposed, and resolved into its compo- 
nent parts. This is most easily done, by having a 
gun barrell c c, B, containing shavings of iron, to 
one end of which a retort, A, is fixed, the other 
terminating in a water-trough, d ; the tube being 




passed through a furnace B.* On applying heat to 
the retort, the water, being converted to vapour, 
passes through the tube, and is decomposed, an 
elastic fluid, or gas, will come out at the opposite 
end, and may be collected in a jar ; it is hydrogen, 

* The cut represents a more perfect arrangement, for the purpose of condensing 
any vapour which may pass through undecomposed, i» the worm d ; it drops into the 
bottle 5, and the gas passes off through/. 



WATER. 147 

ss may be shewn by its inflammability. If the iron 
be removed from the tube, and weighed, it will be 
found heavier than before; and it may, by particular 
means, be made to afford oxygen, or, by heating it 
vyith other substances, compounds are formed, which 
are known to contain it. In this experiment, the 
oxygen of the water has combined with the iron; 
while the other ingredient, the hydrogen is set free. 

WATER. 

Water is a very important agent, not so much 
from the attraction which it exerts for other sub- 
stances, as from its communicating to them that 
fluidity so necessary for their successful operation ; 
and so little does it alter their affinities, that in 
most cases its action is entirely overlooked. When 
pure, it is destitute of taste, smell, and colour. Its 
specific gravity, and capacity for caloric, it has been 
already stated, are called 1000, being used as the 
standard of comparison. By the addition or abstrac- 
tion of heat, it does not suffer any change, except in 
form, freezing at 32, and, under the usual pressure, 
boiling at 212. — See Fluidity and Evaporation. 
If the water be not pure, such as when it holds s^ 
salt in solution, the boiling point is higher, the 
degree depending on the salt, and the quantity dis- 
solved ; and in these cases, the temperature of the 
vapour is the same as that of the fluid from which it 
is formed. Hence a method of increasing the heat 
to be given to a body, by a water bath, or by steam, 
by dissolving a salt, as sea salt, nitre, or potassa, in 
the water. 

The action between water and atmospheric air is 
very important, as under it is included the considera- 
tion of what is called spontaneous evaporation, and 
the formation of rain, hail, snow, dew, and hoar frost. 

Almost all fluids, when exposed to the air, dimin- 
ish in weight ; and, if for some time, they disappear, 
they are said therefore to disappear spontaneously, 



14$ ^ELEMENTS OP CHEMISTRY. 

and the process is called spontuneous evaporation^ 
to distinguish it from evaporation by the application 
of heat. 

Fluidsj when exposed to the air, disappear with 
different degrees of celerity. Water is dissipated 
slowly, spirit of wine quickly, and the volatile fluid 
ether, still more so. The lower the boiling point, 
in general the fluid evaporates more speedily. By 
increasing the surface, the evaporation goes on more 
quickly. Hence, when we wish to cause a fluid to 
disappear soon, it is put into a shallow vessel. A 
certain quantity of a substance can evaporate in a 
given bulk of air ; and the less of it previously con- 
tained in the air, the quicker is the evaporation. 
When it has taken up as much as it can contain, it is 
then said to be saturated. By changing the air, there- 
fore, exposed to the surface of the fluid, the evapora- 
tion is increased 3 hence the effect of wind in quicken- 
ing evaporation, and in drying a moist body. By 
elevating also the temperature of the air, it can retain 
more of the fluid, and the quantity taken up increases 
in a greater ratio than the increase of temperature. 

When the air, thus loaded with moisture, has 
its temperature cooled, as by exposing it to a cold 
object, part of that which it detains is deposited. 
Hence it is, that in crowded rooms, in which the air 
is loaded with watery vapour, given off chiefly by 
respiration, the windows and walls, which are colder 
than it, are always moist. It is in this way that we 
can account for the formation of rain, hail, snow, 
dew, and hoar frost. When, by any means, the 
atmosphere of the higher regions has its temperature 
diminished, it loses in part the power of holding the 
watery vapour in solution, which is therefore set 
free. If the change be not great, rain may be the 
consequence ; but if the reduction of temperature 
be considerable, snow or hail may fall. When the 
temperature of the atmosphere is more gradually 
reduced, dew or hoar frost may be produced. The 



HYDROGEN BLOW-PIPE. 



149 



deposition of dew is easily shewn, by exposing a 
bottle with cold water in a room ; its sides very soon 
become moist. If the bottle be filled with a mixture 
of ice and salt, the moisture in the atmosphere is 
deposited on it, but it then assumes the form of hoar 
frost, being frozen by the cold of the mixture. In 
the same way, when the air immediately in contact 
with the ground, or with trees, or other objects, is 
by any means cooled, it deposits either dew or hoar 
frost, according to the temperature of these objects. 
See page 102. 

It has been already said, that when hydrogen and 
oxygen are mixed in proper proportions, and heat 
applied, they explode. If, after being mixed, they 
be allowed to flow in a small stream, and kindled, 
they excite a very intense heat, perhaps the most 
intense we have yet been able to produce. This 
constitutes what is called the oxy-hydrogen blow- 
pipe,^ When the gases were first used for this pur- 
pose, they were kept in separate vessels, and forced 
out by a column of water, a pipe proceeding from 
each vessel, and terminating by a common aperture. 
An instrument has been lately constructed, into 

which the mixture is 
forced by a cendens- 
ing syringe, and from 
which it again issues 
when the stop-cock is 
opened. It consists 
of a strong copper 
box, a, to which there 
is adapted a stop-cock, 
6, terminated by a 
very fine aperture, c 
is the condensing syringe, by which the gases are 
thrown from the bladder, rf, into the box. When 
full, having shut the cock,e, the syringe is removed. 
On opening the cock, *, the gas issues ^ith great 

*ror a description of Dr Hare's and other blow-pipes, see Manual, p. 106. 
13^ 




150 ELEMENTS OF CHEMISTRY. 

force, and may be kindled. When this apparatus 
was first used, dangerous explosions often happened, 
owing to the flame rushing into the box, and setting 
fire to the gases. Many improvements upon this 
instrument have been suggested, one of which is by 
safety tubes, which are merely a number of very 
fine tubes, or, which answers equally well, several 
folds of fine wire gauze, both of which allow the gas 
to escape, but prevent the admission of the flame. 
These are placed in a small box attached to the cock, 
y*, with a small reservoir for oil, through which the 
gas passes, and which, should the flame by any 
means get through the gauze, puts a stop to its 
progress inwards When the flame of the gas is 
impelled against a piece of iron placed on charcoal, 
it is very soon melted, and thrown about in beautiful 
sparks. The heat excited is even sufficient to melt 
tlie earths. Thus, if a piece of tobacco pipe is held 
at the point of the flame, it is instantly melted ; and 
if this be done in the dark, the light is very intense, 
so much so, that it is impossible to bear it for any 
time. Though by this apparatus we can act only on 
small objects, yet it affords an excellent method of 
ascertaining the efiects of an intense heat on different 
bodies. These will be enumerated, when giving the 
chemical history of those that have been subjected 
to its action. 

Hydrogen, from its extreme lightness, is employ- 
ed for filling balloons. A balloon is merely an ^ir 
tight bag, made of some very light material, so that 
when filled with hydrogen, it is lighter than its 
own bulk of air, consequently, when left to itself, it 
rises, just as a cork would rise from the bottom of a 
j^r of water. An easy method of shewing the as- 
cent of a body filled with this gas, is the familiar in- 
stance of a soap bubble, which ascends when let ofi* 
from a tobacco-pipe, attached to a tube coming from 
a gas holder of hydrogen, the soap bubble being filled 
with it, instead of the air from the lungs, as in the 



HYDROGEN LAMP. 151 

common method of forming it. Balloons are made 
of oiled silk, rendered air tight by being covered 
with varnish. That commonly employed is India 
rubber, dissolved in oil of turpentine. As a sphere 
presents less extent of surface in proportion to its 
contents, than any other figure, it is of course the 
best for a balloon ; but they are seldom made of this 
form ; they are in general of a pear shape, the point 
being kept down. The hydrogen is prepared from 
a mixture of oil of vitriol and water, with pieces 
of old iron. These are mixed in barrels, made air 
tight by clay, from which there proceed tubes, that 
join with the mouth of the balloon. 

Hydrogen gas is now employed as a means of 
procuring a light. This was formerly done by elec- 
tricity, but the apparatus, besides being costly, is 
difficult to manage, and apt to get out of repair. A 
much more easily managed, and less expensive 
method, is by the action of platinum. Platinum is 
soluble in aqua regia, and by the addition of sal-ammo^ 
niac to the solution, a brown powder is precipitated, 
which, when subjected to a red heat, aflfords metallic 
platinum in a spongy state. See Platinum. When 
this is exposed to hydrogen gas, it absorbs it with 
great rapidity, and becomes red hot, so that if air be 
present, the gas is kindled. Hence, if a stream of 
hydrogen be propelled against a small piece of the 
metal, it is almost instantly inflamed, and thus a light 
may be procured. Different forms of the appara- 
tus have been emplo3^ed for this purpose. Perhaps 
the most convenient is the following. It consists 
of two vessels, a and b, a is a bottle 
with three apertures ; into c is placed a 
stopper to which a rod of zinc, d, is 
fixed. From e there proceeds a tube, 
with a stop cock, having a very fine open- 
ing placed immediately opposite a little 
box, y, containing the platinum. The 
vessel; 6, terminates by a tube^g-; which 




152 ELEMENTS OF CHEMISTRY. 

passes nearly to the bottom of a. Having filled a 
with a mixture of oil of vitriol and water, 1 to 8, 
the zinc rod is to be introduced, by which the water 
is decomposed, and hydrogen is disengaged. As it 
rises to the top of a, it depresses the fluid in it, and 
makes it ascend into b ; but the moment it gets be- 
low the end of rod, d^ the action stops, while at the 
same time, the mouth of the pipe, g^ being below 
the fluid, there is no escape of gas. On opening the 
stop-cock, the gas rushes out, and coming on the 
platinum, is kindled ; the fluid at the same time falls, 
and getting on the zinc generates more hydrogen. 
We have thus, then, always a constant store of gas, 
subject to the pressure of a column of fluid, by which 
it may be forced out. 

The distance at which the platinum must be placed, 
in these instrumxents, depends on the pressure, and 
the size of the aperture of the cock ; it must there- 
fore be found by trial. In general, half an inch is 
sufficient. 

Hydrogen exists in all animal and vegetable 
bodies, and is given out by them during putrefaction. 
Hence it is found in marshy situations, and over 
stagnant pools. Its chief source, however, is water, 
from which it is always obtained, by the processes 
already described. 

CHARCOAL, OR CARBON. 

Charcoal is in general prepared by collecting a 
quantity of wood into a heap of a conical form, 
with a base of about 15 or 20 feet, and 8 or 10 high. 
It is covered with turf, and then kindled ; and after 
the flame seems to have reached the whole of it, the 
admission of the air is prevented as much as possible 
by putting on more turf. The combustion is thus 
allowed to go on slowly and imperfectly, by which 
the wood loses its watery and gaseous part, and is 
completely charred. As thus prepared, it is light 
and porous, and retains the form of the wood from 



CHAR<;OAL OR CARBON. 153 

which it is obtained. A much purer charcoal is 
now procured, by subjecting wood in la^ge cast iron 
cylinders to a red heat, so as to exclude it from the 
action of the air. When the whole of the gaseous 
ingredients are disengaged, the fire is extinguished, 
and the charcoal allowed to cool in the cylinders, or 
it is removed from them and instantly put into iron 
boxes, in which it is kept excluded from air till quite 
cold. During this process, carburetted hydrogen 
gas, and watery vapour, are given off, the former 
produced by the union of carbon and hydrogen, and 
the latter by the union of hydrogen and oxygen, 
existing in the wood. At the same time, there is 
disengaged a considerable quantity of impure acid, 
called pyroligneouSy and which, by distillation, 
yields vinegar. See Vinegar. 

Charcoal is a very bad conductor of heat ; it is 
therefore much employed for confitiing it in furna- 
ces, and in tubes, which convey warm fluids. Tims, 
the insides of furnaces are frequently lined with a 
mixture of charcoal and clay, which is protected 
from the fire by a coating of clay and sand. It has 
also been recommended, that vessels for holding 
fluids warm should be made double, and the interven- 
ing space filled with powder or charcoal, so that little 
of the heat may pass off. 

Charcoal is not liable to putrefy ; hence it is cus- 
tomary to char the end of the stakes that are to be 
driven into the ground, by which they are not only 
preserved, but penetrate the earth more easily. 
Charcoal also possesses the remarkable property of 
depriving bodies of their colour, taste, and smell. 
When water has become putrid, from having been 
kept long in wooden vessels, it is deprived of its 
putridity, by filtering it through charcoal in powder, 
a method often resorted to in long voyages. For 
this purpose, a quantity of it is put into the casks, 
and, after being shaken, the powder is allowed to fall 
to the bottom^ and the water may be drawn off clear. 



154 ELEMENTS OF CHEMISTRY. 

Abetter mode, however, and the one usually prac- 
tised, is to char the inside of the cask, by which 
putridity is entirely prevented. Malt liquor, by 
being mixed with charcoal, is also deprived of its 
colour, and the disagreeable flavour it usually has 
when recently prepared. Putrid animal matter like- 
wise loses in a great measure its unpleasant taste 
and odour, by rubbing it with charcoal powder, and 
allowing it to remain on it for some time. For the 
success of these different processes, the charcoal 
ought to be newly made ; and if it has been kept for 
some time, it must be exposed to a red heat, and 
excluded from the air till cold. For some of them, 
particularly for removing colour, animal charcoal is 
preferred. That sold under the name of ivory 
blacky procured by exposing ivory or bone to heat, 
is generally employed. 

When charcoal is heated in contact with air, it 
burns, and, if well prepared, without flame and 
smoke ; but, as usually made, it at first gives off both, 
the emission ceasing in a short time. After this, it 
gives^ a steady heat, and is much used in chauffers 
and furnaces, as by dyers, confectioners, &c. Though 
there is no smoke^ yet the air is vitiated during the 
combustion, a transparent colourless aeriform sub- 
stance called carbonic acid or fixed air^ is formed 
by the union of the carbon with the oxygen, which 
does not support combustion, and which speedily 
proves fatal when breathed. That the qualities of 
,;^^^ the air are changed is easily shown, by 
^>^^Nw holding a jar, a, over a chauffer of char- 
' ^ coal, b, for a few minutes; the product of 

the combustion rises and fills it, and if, 
after removing it, and placing a plate at 
the bottom of it, a lighted taper is intro- 

H^" ^ duced at r, it is instantly extinguished. 
Charcoal, it has been already said, is 
employed for affording heat. It is used 
also for procuring many of the metals from 



CARBTJRETTED HYDROGEN. 155 

their ores, and in the preparation of gunpowder. 
It is used instead of pencils, for taking sketches, 
any inaccuracy being easily rubbed out. For this it 
ought to be prepared from willow, w^hich affords it of 
uniform softness. When employed as black paint, 
it should be made from ivory, as this seems to give 
the most intense and durable black. 

The substance sold under the name oilanip blacky 
is merely the soot collected during the burning of 
the refuse of pitch, or tarry matter. A very fine 
kind of charcoal may also be procured, by holding a 
plate in the flame of a lamp, by which it is covered 
with soot, which may be removed, and the plate 
again held in the same situation, so that, by repeat- 
ing the process, a quantity of it may be collected. 
When the charcoal is required very pure, as for some 
of the finer paints, that prepared from ivory, or by 
the process last mentioned, should be washed with 
muriatic acid, or weak aquafortis, by which the 
whole of the impurities are removed. Charcoal, 
prepared in this way, is employed for affording china 
ink. For this purpose, 6 parts of isinglass are dis- 
solved by boiling in 12 of water ; 1 of Spanish 
liquorice is dissolved in 2 of water, and mixed with 
the former, \v\\h which one of ivory black is to be 
intimately incorporated, and the whole evaporated 
to the proper consistence. 

CARBURETTED HYDROGEN. 

It has been already mentioned, that hydrogen gas 
is found in considerable quantity in coal mines. 
another elastic fluid, of nearly the same properties, 
also issues from the chinks in the coal. It is a com- 
pound of carbon and hydrogen, from which it has 
received the name of car^buretted hydrogen. It is 
sometimes, also, called coal gas, and by miners Jire 
damp. It is transparent and colourless j of course, 
invisible. Its specific gravity is only 555^ air being 
1000. When heated in contact with air, it burn: 



156 ELEMENTS OP CHEMISTRY. 

with a reddish flame; and, during its combustion 
affords water, and carbonic acid gas, — the former 
generated by the union of its hydrogen with the 
oxygen of the atmosphere, — the latter, by the carbon, 
and oxygen combining. If the gas be mixed with 
air, and more particularly with oxygen, in the pro- 
portion of one of gas to two of oxygen, and heated, 
it explodes with considerable violence, the whole of 
its ingredients uniting with the oxygen, to form 
water and carbonic acid. 

Carburetted hydrogen is produced very abundantly 
in nature. It is emitted by some stagnant pools; 
but its chief source is from the coal in mines, through 
the chinks of which it issues, in some mines, in 
great abundance ; and as it is lighter than atmos- 
pheric air, it ascends, mixing with it as it rises. As 
it increases in quantity, it gradually occupies more 
and more of the mine, till it reaches the lights used 
by the miners, by which it is inflamed, and, from the 
immense quantity of it, it explodes with tremen- 
dous violence, and produces the most dreadful con- 
sequences. The discovery of a means of prevent- 
ing this evil, for many years occupied the attention 
of several distinguished philosophers, but without 
success. Attempts were made to ventilate mines 
thoroughly, that by keeping up a constant change of 
air, the inflammable gas might in a great measure be 
carried away. When this could not be done miners 
used occasionally to set fiire to the gas, before much 
of it was collected; at the same time, the person 
who kindled it stood in water, and the moment he 
thrust the candle into it, he plunged under the fluid. 
By these means, the dreadful consequences of the 
explosion were in a great measure prevented. 
There was still, however, cause to regret, that they 
occasionally occurred, perhaps from the carelessness 
of the workmen, or frojn the greater emission of gas 
at one time than another. We can now, however, 
boast of a preventive of these fatal explosions, iii 



SAFETY LAMP. 157 

the safety lamp of Davy, which has now been prov- 
ed, by the most ample trials, to avert completely 
the danger arising from using lights in coal mines, 
even though abounding with an explosive mixture. 
In his experiments, made with a view to ascertain 
how to prevent explosion in mines, Davy discovered 
that flame would not pass through very small tubes 
of glass, or metal, nor through very fine wire gauze. 
He therefore concluded, that to light mines, in 
which there is a collection of inflammable gas, it is 
merely necessary to have a lamp so formed, that the 
air requisite for the combustion should enter through 
minute apertures. In the first lamp he employed, 
the air was allowed to pass through a piece of wire 
gauze placed at the bottom, the flame, as usual, being 
surrounded by glass or horn. He afterwards found, 
however, that if a lamp, surrounded on all sides by 
wire gauze, ba put into an inflammable mixture, the 
air necessary for the combustion enters through the 
holes of the gauze, taking along with it the inflam- 
mable gas, which is also consumed, but the flame 
does not communicate to the explosive mixture with- 
out. The lamp was therefore constructed in this way. 
After being kindled, it was exposed to a mixture 
of air and carburetted hydrogen in a mine, which, 
passing through the gauze, was kindled by the flame 
of the lamp, and burned ; and as there was a constant 
renewal of it, not only light was thus afibrded, JDut 
the destructive element, the carburetted hydrogen, 
was itself consumed. When the gas is mixed with 
about 12 of air, the flame of the lamp continues 
within that of the gas ; but when there is only about 
7 of air, the flame of the wick is extinguished, but 
that of the gas continues, and thus also afibrds light, 
which, though feeble, is sufficient for some purposes. 
Though wire gauze is thus a preventive to the 
passage of ffame, yet, should the wire become red 
hot, provided it be of sufficient thickness, it may 
set fire to the gas. It is necessary^ therefore, to 
14 



158 



ELEMENTS OF CHEMISTRY. 



/^ 



mmsastsm 



4 



-6 



have it of the requisite size ; about the ^-^ih^ or 
-§^\h of an inch, is found to be the best ; and to 
prevent any danger arising from the overheating 
of the wire, as that above the flame of the wick is 
the only part likely to become so, the gauze has a 
double top ; so that, should that immediately over 
the flame become red hot, it will explode the gas 
above it, or that between the inner and 
outer top. a is the lamp, with its flame, b. 
c is the cylinder of gauze, terminating 
with a top at d ; and over this is another 
cylinder, 6, coming down over c, about 
an inch. There must also be at least a 
certain number of holes in the square 
inch ; from 500 to 600 have been found 
to answer best. 

That there is no danger in putting thislamp into an 
explosive mixture of air and carburetted hydrogen, 
may be easily shewn on a small scale. Having filled 
a gas-holder with the gas, the flexible -f-pp 

tube, «, coming from it, must be pass- 
ed through a hole in a stool, 6, and 
over this is to be placed a glass, c, open 
above and below, in which the lamp 
is suspended, the upper aperture be- 
ing covered with a piece of paper or 
cloth. On opening the cock, so as to 
allow the gas to flow in very gradual- 
ly, it displaces a part of the atmos- 
pheric air, so that there is an explosive mixture in 
the jar, which is constantly passing into the lamp, 
through the holes in the gauze, by which the com- 
bustion is kept up, and as the mixture is consumed, 
the jar being open below, there is a constant admis- 
sion of air, to be mixed with the gas coming from 
the pipe. In this experiment, when the air is in 
considerable quantity, the flame of the lamp is seen 
within that of the gas, with which the cylinder of 
gauze is filled j but when the air dinainishes, the for- 



E==i 




tzi^^a 



OLEFIANT GAS. 159 

mer is extinguished, but the latter continues as long 
as the proper proportions can be kept up. affording 
a beautiful flame within the gauze, and which does 
not pass through to the explosive mixture by which 
the lamp is surrounded. See Manual, p, 195. 

That wire gauze is a preventive to the passage of 
flame, may be shewn still more easily. If we set 
fire to a jet of gas, and hold a piece of gauze over 
it, the flame is seen only below, provided we do not 
keep the same part always over the flame, for, in this 
case, the wire becomes red hot, and kindles the gas 
above. Or if a jet of gas be allowed to pass through 
the gauze, and be kindled above, the flame does not 
communicate to that below. See Manual^ p, 57. 

Carburetted hydrogen is not put to any particular 
use. When required for experiments, it is prepared 
bypassinrg steam over red hot charcoal, using the 
same apparatus as that for procuring hydrogen by 
the action of a red hot iron, [see page 146) with this 
difference, that the tube must be stuffed with pieces 
of charcoal, instead of shavings of iron. When the 
charcoal is properly heated, the water in the retort, 
is made to boil, by which the vapour passes through 
the tube, and is decomposed ; the hydrogen unites 
with part of the carbon to form carburetted hydrogen, 
while the oxygen, the other ingredient, is combined 
with the remainder, to form carbonic acid. These 
come off together, and may be collected in jars, 
or a gas holder may be filled with it, by putting the 
mouth of the tube into it. To remove the carbonic 
acid, it is merely necessary to have the jars, or the 
gas holder, filled with lime water, the lime of which 
unites with it, so that the carburetted hydrogen is 
thus obtained pure. 

OLEFIANT GAS. 

Carbon and hydrogen unite in other proportions, 
and form what is commonly called olefiant gas^ 



160 



ELEMENTS OP CHEMISTRY. 




from its forming an oily looking fluid, when mixed 
with another gas, the properties of which have not 
yet been described. It does not exist any where in 
nature ; we are obliged, therefore to procure it by 
the decomposition of substances, containing its com- 
ponent parts. For this purpose, 2 measures of oil 
of vitriol are mix- ^ — v 
ed with 1 of spirit ' - » 
of wine, in a re- 
tort, «, and by the 
application of the 
heat of an Argand 
lamp, the alcoho 
is decomposed, anc 
the gas is given off? and may be collected in the jar, 
b. Alcohol contains oxygen, hydrogen, and carbon, 
as its ingredients ; and by the action of the acid, 
aided by heat, these enter into a new state of com- 
bination, part of the hydrogen and carbon combine, 
and form the olefiant gas. This gas, then, contains 
the same ingredients as carburetted hydrogen, but it 
has a larger proportion of carbon, -»-it contains twice 
as much ; and hence it is frequently called bicarbu- 
retted hydrogen, from the Latin word bis, signify- 
ing twice. It is transparent and colourless. When 
heated in contact with air, it is kindled, and burns 
with a bright white flame, by which it is easily dis- 
tinguished from other gases ; and during its combus- 
tion, it affords carbonic acid and water, both of its 
ingredients, carbon and hydrogen, uniting with the 
oxygen of the air, the former to yield the acid, the 
latter the water; and as it contains twice as much 
carbon as common caburetted hydrogen does, it of 
course affords twice as much carbonic acid by its 
combustion. When mixed with oxygen, in the pro- 
portion of 1 of gas to 3 of oxygen, it explodes with 
great violence ; hence it takes a larger proportion of 
oxygen, of course also of atmospheric air, for its 
combustion, than the other. 



CHLORINE, OR OXTMURIATIC ACID. 161 

Olefiant gas, and carburetted hydrogen, are formed 
during the decomposition of coal and oil by heat, 
by which coal gas and oil gas are procured ; but 
besides these, other substances are also formed, and 
materials are employed in the processes, the proper- 
ties of which have not yet been detailed. The pre- 
paration and quality of these gases will therefore be 
described, when these substances have been consid- 
ered. See Coal and Oil. 

CHLORINE, OR OXYMURIATIC ACID. 

When spirit of sea salt, or muriatic acid, is poured 
on some bodies that contain oxygen, as the oxide of 
manganese, and a slight heat is applied to the mix- 
ture, a gaseous fluid is given off, which is possessed 
of very remarkable properties. It is chlorine^ or 
oxymuriatic acid, the former name derived from the 
Greek word chloros, signifying yellowish green^ 
which is the colour of the gas ; the latter, because it 
w^as at one time supposed to be a compound of oxy- 
gen and muriatic acid. For preparing it, 1 part of 
the oxide of manganese in powder, is put into a re- 
tort, Gf, (see opposite page) and 4 parts of muriatic 
acid are poured on it. On applying the heat of a 
spirit or Argand lamp, an action commences, and the 
gas is disengaged, and collected in jars, 6, filled 
w4th, and inverted over warm water. This gas 
is now generally considered a simple substance, be- 
ing set free by the decomposition of the muriatic 
acid, which is a compound of it and hydrogen, the 
oxygen from the manganese uniting with the hydro- 
gen to form water, and setting free the other ingre- 
dient, the chlorine. This elastic fluid is of a yellow- 
ish green colour, by which it is easily distinguished 
from the others already described. It is much 
heavier than air, its specific gravity being 2500 to air 
as 1000. It has a disagreeable offensive smell, and is 
extremely irritating to the eyes, nostrils, and lungs. 
When breathed pure, it instantly extinguishes life ] 
14^ 



162 ELEMENTS OP CHEMISTRY. 

even when largely diluted with air, it excites head- 
ache, severe coughing, and pain of the chest, so that 
great caution is necessary when experimenting with it. 
Chlorine possesses a wonderful power over inflam- 
jnables. It has been already said, that some bodies, 
as phosphorus and iron, burn with great splendour 
in oxygen ; in this gas they are, in general inflamed 
when put into it, though they do not burn with 
nearly so much splendour. Thus ^-^ 

when some of the metals in leaf, as /^^ d\ 
brass, «, is put into a bottle of it, it is 
instantly kindled. Here it is neces- 
sary to put the bottle into a plate, 
with water, c, and cover it with a bell 
glass after the introduction of the leaf, ^" 
to prevent the gas from escaping. ^ 






Chlorine is easily absorbed by water, the solution 
has the odour of the gas, and possesses, in a remark- 
able degree, the power of depriving bodies of their 
colour. If, for instance, the solution be added to 
any vegetable infusion, as that of red cabbage or 
litmus, the colour instantly disappears, and, what is 
also remarkable, it cannot be recalled by the action 
of any other substance. The same takes place when 
the solution is added to the colouring matter derived 
from the animal kingdom, as cochineal. If the col- 
our has been imparted to cloth, it cannot resist the 
effect of chlorine. If a few pieces of coloured cloth 
be put into the solution, they will also become white, 
the time required depending on the nature of the dye 
stuff. 

From this remarkable property, chlorine is now 
employed with the utmost success in bleaching. 
When introduced for this purpose, it was used in the 
form of gas, and afterwards in solution in water, but 
these, though very eflScacious, were found to be 
extremely injurious to the workmen ; the process 
has therefore undergone several alterations and im- 
provements, the principal of which consists in com- 



SULPHUR. 16S 

bining the chlorine with lime, so that it is in a great 
measure deprived of its noxious effects, and can be 
transported with greater ease from the manufactory 
to the bleaching ground. In the process of bleach- 
ing, several substances, as acids and alkalies, are 
used, the properties of which have not yet been de- 
tailed. It will therefore be described afterwards. 
See Lime, 

SULPHUR. 

Sulphur, or Brimstone^ is generally in cylinders, 
or in fine powder, commonly called flowers of sul- 
phur, and which is by far the purest. It has neither 
taste nor smell, but when rubbed, it has a faint pecu- 
liar odour. Its specific gravity is 1990, compared 
to water as 1000. When a slight heat is applied to 
the sulphur in cylinders, as by holding it in the 
hand, it crackles and soon falls to pieces. When 
heated to about 220, it fuses, and acquires a reddish 
colour. It is remarkable, however, that if the heat 
be continued after it is melted, instead of remaining 
in that state, it becomes thicker, which change com- 
mences at about 320, and it continues so, to about 
550, at which it passes off in vapour. As it cools, 
it again becomes quite fluid, and continues so till 
it is congealed. If, when fluid, it be poured into 
water, it does not instantly become hard, but viscid, 
and remains so for about a quarter of an hour. It is 
in this state, that impressions from seals and medals 
are often taken with it. For the success of this 
experiment, it is necessary that the sulphur be kept 
in a close vessel, or in one with a small mouth, as 
a common Florence oil flask, to prevent the ir^Q 
admission of air. If the temperature be raised above 
550, it passes into vapour, which is condensed, as 
its temperature falls; hence the method of preparing 
the flowers, or sublimed sulphur. When heated to 
about 300° in air, it takes fire, and burns slowly, 
Avitli a pale blue flame^ during which fumes are given 



164 ELEMENTS OP CHEMISTRY. 

off, that are very offensive. They are a compound 
of sulphur, and the oxygen of the air, and possessed 
of acid properties. It is sulphurous acid,, or what 
is commonly called the fumes of sulphur^ and 
which, though considered an acid, destroys colouring 
matter; and hence its use in some kinds of bleach- 
ing, particularly for cleaning straw for bonnets. 

When the temperature to which the sulphur is 
subjected is high, as when it is thrown on a red hot 
plate of iron, it burns with a much brighter flame, 
and is more rapidly consumed, giving off fumes 
which are also very offensive, though perhaps not 
so much so as the former; but when condensed, th^y 
are much more corrosive. This is the well known 
substance, sulphuric acid,, or oil of vitriol^ the pro- 
perties of which will be afterwards described. 

The action between sulphur and phosphorus is 
important, as they unite and form a substance, very 
easily kindled, merely by exposure to air. When 
they are heated slightly together, excluding the air, 
to prevent the combustion of the phosphorus, they 
combine, but the experiment performed in this way 
is dangerous, as, even with all precautions, the mix- 
ture sometimes take fire. By far the safest method 
of uniting them, is to put them into a phial, and, after 
corking it tightly, set it aside for some days, by 
which they slowly enter into union. When a little 
of the product is removed, and exposed, to the air, 
it instantly takes fire, and hence its use in affording 
a light. For preparing the instantaneous light' 
giving bottles, apiece of phosphorus well dried is put 
into a quarter of an ounce phial, with about an eighth 
part of its weight of the flowers of sulphur, and then 
well corked, and set aside for a few days, to allow 
them to unite. When a light is required, a little of 
the product is brou2;ht out by a common sulphur 
match, on which, when exposed to the air, it is 
kindled, and sets fire to the sulphur. In using these 
bottles, the cork must be left out as short a time as 



SULPHUR. 165 

possible, to prevent the mixture from absorbing air, 
by which it may be inflamed. They may also be 
more quickly prepared, by putting the phial with 
the mixture into warm water, so as to melt the 
phosphorus, and cause it to act on the sulphur ; but 
as has been already mentioned, unless very cautious 
in heating it, the mixture is apt to take fire, so that 
the other, unless required for immediate use, is 
preferable. 

Sulphur is found in abundance in the mineral 
kingdom, both combined and in its free state. It 
exists in all volcanic countries, as Italy, Sicily, and 
Iceland, which supply the most part of Europe with 
it. It is found also in great abundance in union 
with many of the metals, as iron, copper, and lead. 
Different methods are followed for procuring it, 
according to the state in which it exists. .When it 
is combined with earthy matter, as in volcanic pro- 
ductions, it is exposed to heat, in large pots, well 
covered, to prevent the admission of air; when fluid, 
the impurities fall to the bottom, and it is then pour- 
ed into moulds, thus forming the cylinders. If the 
foreign matter should not separate in this way, a 
greater heat is applied, and the sulphur is sublimed, 
the process being conducted in pots having receivers 
adapted to them, in which the vapour is condensed. 
In procuring metals from their compounds with 
sulphur, they are exposed to heat, by which sulphur 
in vapour is given ofi*, and condensed in chambers 
connected with the vessel, in which the metallic 
compound is heated. 

The uses of sulphur are numerous and important. 
It is employed largely in the preparation of oil of 
vitriol, and in the manufacture of gunpowder, in 
both of which it is used along with nitre. — See 
Nitre, It has been already said, that when, burned 
slowly, it gives ofl" fumes, which are used in cleaning 
straw. For this purpose, the straw, or bonnet, after 
being welted, is suspended in rooms, or boxes, in 




166 ELEMENTS OF CHEMISTRY. 

which the sulphur is burned in small dishes; the 
fumes are absorbed by the moisture, and act on the 
colouring matter, gradually destroying 
it. The action of the fumes of sulphur 
is beautifully illustrated, by suspending 
a rose, a^ in the upper part of a glass 
jar, and placing it over a dish with 
burning sulphur, 6, leaving an opening 
below, for the admission of air. After 
being left in for some time, the colour 
gradually disappears. The same may 
be done also with many other flowers, 
or with a leaf of red cabbage. Though 
the colour is thus banished, it is not 
destroyed ; it may be recalled by the action of a 
strong acid. If, for instance, the rose or cabbage- 
leaf be put into water, previously mixed with a little 
oil of vitriol, it again becomes red. It is remarka- 
ble, also, that if a living plant be exposed to the 
fumes, though the colour disappears, the plant is not 
in the least injured ; hence a method of having white 
and red roses on the same plant, by exposing some 
of them only to the fumes. 




ACIDS. 

It has been already mentioned, when describing 
the properties of the simple bodies, that they form, 
by their union with others, a distinct class of com- 
pounds called acids. The acids possess properties 
by which they are easily distinguished from other 
substances. They have a sour taste, and most of 
them are very corrosive ; but their distinguishing 
feature is, their changing the vegetable colours to 
red. If a few drops of oil of vitriol, aquafortis, or 
muriatic acid, be added to purple cabbage water, it 
becomes red. The same is the case if they be add- 
ed to other vegetable colours, as litmus, violets, &c. 



NITRIC ACID. 



167 



Hence these are employed as tests of acids ; that is, 
to ascertain when they exist in any substance. We 
may add the infusion to the fluid in which we are 
trying to detect an acid ; but a more convenient 
method is, to have them spread on paper and dried. 
If a slip of this be put into a fluid, in w^hich there is 
an acid, it instantly becomes red. 

NITRIC ACID. 

Nitric Jicidy in its impure state, however, has 
been long known, and in use in the arts under the 
name aquafortis. When pure, it is a transparent 
colourless fluid. As commonly purchased, however, 
it is of a yellowish or brovvnish colour, in which statf 
it is called nitrous acid. It has a peculiar odour| 
and sour taste, and possesses, in a remarkable degree, 
the properties of acids. It is very corrosive, — a 
drop of it falling on the skin instantly destroying it, 
and occasioning pain. Like other acids, it reddens 
vegetable blue infusions. Nitrous acid acts with 
very great ease on most inflammables, to which it 
communicates oxygen. Thus, if a metal, as iron, be 
put into it, the iron acquires oxygen, and is convert- 
ed into an oxide. This experiment shews that oxy- 
gen is one of the ingredients of the acid. It has been 
proved, in diflferent ways, that it is a compound of 
oxygen and nitrogen, the same ingredients as those 
of the atmosphere, but with a much larger proportion 
of the former. Thus, if electric sparks be passed, 
for a considerable time, through air, confined in a 
jar, its elements enter into union, and nitrous acid 
is formed. Or, if the vapour of the acid be passed 
from a retort, a, through a red hot earthen tube, c, 



r\ 






l2^ 



168 ELEMENTS OF CHEMISTRY. 

a gaseous fluid comes out at the opposite end. and 
which is a mixture of oxygen and nitrogen; for, 
when collected in the jar, e, and a lighted taper is put 
into it, it burns with nearly the same splendour as in 
oxygen, and after the combustion has ceased, there 
remains a gas, which is nitrogen. 

Nitrous acid is employed in the state of vapour 
for purifying apartments, as those of hospitals, or of 
dwelling-houses, in which fever patients have been 
confined, and it is used also for preventing con- 
tagion. — See Nitre. It is employed also for etching 
on iron and copper. For this purpose, the plate, 
suppose iron, after being well polished, is covered 
with a thin coating of a substance that will resist 
the action of the acid. That generally employed, 
is prepared by dissolving asphaltum in essential oil 
of turpentine. It is kept liquid, and applied to the 
plate in this state, from which the oil evaporates, 
and leaves the other, giving it a thin coating. The 
acid is generally mixed with strong vinegar, or 
pyroligneous acid, and spirit of wine, in the propor- 
tion of equal measures of acid and alcohol, to 4 of 
vinegar. The vinegar and alcohol are first mixed, 
and, almost immediately after, the acid is put in. 
After the plate has received its coating, and been pro- 
perly dried, the part to be acted on is then exposed, 
by scraping ofi* the coating with a sharp instrument, 
and, having raised a wall of a mixture of bees' wax 
and rosin around the edge of the plate, the acid 
mixture is poured on, and allowed to remain for 
some time, during which it slowly dissolves the 
metal. When the action has continued a certain 
time, the fluid is poured off, and the plate washed 
with whisky. Those parts sufficiently deepened, 
are covered with the coating mixture, and the liquid 
again put on ; and by repeating the process, the 
figure is etched on the plate, those places which 
have been longest exposed to the action of the acid, 
being of course deepest, and giving the darkest 
impression in the print taken from it. 



CARBONIC ACID. 169 

Nitrous acid is used in dyeing, and in other pro- 
cesses, which will be afterwards noticed. For the 
method of obtaining it, see Nitre. 

CARBONIC ACID. 

Carbonic Jlcid, or fixed air, as it is usually called, 
exists in the gaseous form. It was the first aeriform 
substance discovered, difierent from the air of the 
atmosphere. Though it must have been observed 
during many cases of chemical action, it was not 
known as a distinct substance till the year 1755, 
w^hen it was discovered by Dr Black, who gave it 
the name oi fixed air^ from its being found, in its 
condensed state, in union with other bodies. Other 
names were also given it, as aerial acid^ but all of 
which have given way to that of carbonic acidj 
shewing that it is a compound of carbon. Though 
a feeble acid, it is one of very great importance, not 
only from its general difiusion through the objects 
of nature, but from the important purposes it serves 
in the economy of the animal and vegetable king- 
dom. 

It is a transparent, colourless gas, the specific 
gravity of which is much greater than that of air •, 
it is 1527 to air as 1000. It is unfit for 

the support of respiration and combustion, 

'I V. If a lighted taper be put into ajar of it, a, 
1 J it is instantly extinguished. 
^ ^ That this substance is a compound of 
carbon and oxygen, is easily shewn ; we 
have merely to burn carbon in a vase of 
oxygen, a, and, after the combustion is firjished, put 
into it a lighted taper, which will be extinguished. 
Though it may be formed in this way, it is never 
procured so for use ; it is always obtained by the 
decomposition of substances containing it, as chalk, 
or marble, which are compounds of it and li.ne. 
See Lime. 

15 




170 ELEMENTS OF CHEMISTRY. 

Water absorbs carbonic acid gas, though not ia 
great quantity ; the rapidity of the absorption, and 
the quantity taken up, increasing by pressure. The 
solution formed is transparent and colourless, has a 
slightly acid taste, and sparkles when poured from 
one vessel to another ; and if the quantity of gas in 
it be considerable, it effervesces on exposure to air, 
so that the greater part of the gas escapes. 

Carbonic acid is found in nature in a state of 
purity. The air of the atmosphere always contains 
it, though the quantity varies according to circum- 
stances. In general, it is about 1 percent. That air 
contains carbonic acid, is easily proved. Lime has 
a very powerful attraction for it. It combines with 
it, and forms a substance insoluble in water. If lime 
water, then, be poured into a plate, and left exposed 
lo the air for a few hours, it becomes quite turbid, 
and loses entirely its peculiar taste, the whole of the 
lime being deposited in union with carbonic acid. It 
is found in very large quantity in pits in which there 
is not a free ventilation, and is called by miners 
choke-damp ; and it exists also in great abundance 
in some caverns, particularly those in volcanic coun- 
tries. From the collection of carbonic acid in pits 
and mines, fatal accidents have happened from peo- 
ple visiting them when they had not been examined 
for some time, the air being so much loaded with 
this aeriform substance, as to prove fatal when breath- 
ed. Accidents of this nature are, however, owing 
to carelessness, for there is an easy method of know- 
ing whether the air in them will prove injurious, 
which is merely to expose a burning body to it: for 
if the light be extinguished, it will certainly prove 
fatal. It is remarkable, however, that some bodies 
are much sooner extinguished than others, in air 
loaded with it ; thus, a lamp with oil will burn in 
air in which a candle has been extinguished. In 
visiting pits or mines, then, in which there is reason 
to suspect the presence of carbonic acid, a candle or 



CARBONIC ACID. 171 

lamp ought to be carried by the individual ; and so 
long as it burns, there is no danger ; the monnent, 
however, that it is extinguished, all attempts to pro- 
ceed farther ought to be abandoned, because the at- 
mosphere, when breathed for a short time, will 
prove fatal. 

Carbonic acid gas is afforded in great abundance 
by the combustion of substances employed as fuel, 
as coal, wood, and peat ; and that this is the case is 
^ <^r^ proved by holding a jar, «, open above 
^ ^ and below, over a chaufler, h. and after 
keeping it there for some time, remov- 
ing it on a plate at c, and putting a candle 
in at d^ it will be instantly extinguished , 
or if lime water be shaken with it, it 

H^ will become turbid. As carbonic acid is 
given off so abundantly during combus- 
tion, we ought to be very cautious when 
using chauffers, or stoves, particularly in 
apartments in which there is not free ventilation, 
lest the product escaping into the room, and mixing 
with the air, prove injurious to those who respire it, 
which is to be attended to, chiefly in bed-rooms, as 
the gas, when breathed, does not give a person warn- 
ing of his danger, but, on the contrary, gradually 
lulls him into a state of insensibility, from which it 
is difficult. to rouse him. 

Carbonic acid gas is not put to any particular use. 
When in solution, it is employed as a grateful drink, 
sometimes dissolved merely by water, but more fre- 
quently along with soda, and hence it is called soda 
water. As the quantity of gas absorbed is trifling, 
unless when subjected to strong pressure, it is neces- 
sary to have recourse to some means of increasing 
it. For this purpose, the fluid which is to absorb 
the gas, a weak solution of soda, is put into strong 
vessels, into which the gas, gejierated in another, is 
forced, by which a great deal of it is absorbed. 
From this, when fully saturated, it is drawn off 



172 ELEMENTS OF €HEMISTRr. 

into strong bottles, and instantly corked, the cork 
being secured by a wire. In drawing off the fluid, 
however, a great deal of the gas escapes, unless some 
means be taken to prevent it. This is done by hav- 
ing a conical cork which will fit the different bottles 
to be filled. In it there are two apertures, _4-v 

a and 6, the former for the admission of ;—_/ 

the stop-cock from the vessel, the other I'li i/7C 
for the escape of the air from the bottle, lii \\\ 
and over which there is a cover, kept \\\ \\\ 
down by a spring, c. When the bottles a b 
are to be filled, the cork is placed on the stop-cock, 
and then put into the mouth of the bottle ; as the 
water flows in, the air in the bottle is condensed ; 
but when the pressure of this becomes considerable, 
it raises the valve, c, and escapes, so that, the fluid 
being always under pressure, there is little waste of 
the carbonic acid, 

MURIATIC ACID. 

Muriatic Acid^ in its pure state, is a transparent, 
colourless gas, but as employed in the arts, it is a 
liquid, generally of a pale brownish colour, which is 
merely the gas absorbed by water, the colour being 
imparted by impurities, generally a little iron. In 
this state it is commonly sold, under the name of 
marine acid, and spirit of sea salt. When quite 
pure, the liquid acid is transparent and colourless. 
It has an acid taste, and reddens vegetable blue. It 
does not act with any of the substances already de- 
scribed, except with nitrous acid, with which it forms 
the fluid called nitro-rauriatic acid, but long known 
by the name of aqua regia, so termed, as being the 
only solvent of gold. When these acids are mixed, 
there is little or no action at a natural temperature, 
but on the application of a very slight heat, it com- 
mences. Different proportions are employed in 
preparing it, according to the use to which it is to 
be applied. In some instances equal measures, in 
others two of nitrous, and one of muriatic acid, are 



SULPHURIC ACID. 173 

employed. The mixture beingput into a flask, a slight 
heat is applied, the action commences, and is accom- 
panied with the disengagement of a little chlorine, 
and nitrous acid vapour. A dark brown fluid is 
left, which is supposed to be muriatic acid, holding 
chlorine in solution. It is employed for dissolving 
gold, and some other metals, as platinum, the chlo- 
rine which it contains enabling it to act easil}^ on 
them. An impure aqua regia is prepared also by 
dissolving sal ammoniac in nitrous acid, and which is 
very frequently used in the arts. See SalJlmmoniac. 

Muriatic acid is employed for dissolving some of 
the metals, and in the preparation of sal ammoniac. 
It is used also in the form of gas, for purifying 
apartments, and preventing contagion. See Sea Salt. 

Muriatic acid is not presented by nature in a state 
of purity, but it exists in very great abundance in 
combination with other bodies, as in sea salt, and 
many earthy and metallic compounds. Its chief 
source is sea salt^ from which it is always procured. 
See Sea Salt. 

SULPHURIC ACID. 

Sulphuric Jicid^ as usually procured, is a fluid of 
an oily consistence, owing to which, and as it was 
prepared from green vitriol, it has got the name of 
oil of vitriol^ by which it has been long known. It 
is called sulphuric acid, because sulphur is one of its 
ingredients. That sulphur, by its union with 
oxygen, forms an acid, is shewn, by setting fire to 
^./^ it in this gas. For this purpose, having 
V ^ y) kindled a little of it in a cup, «, we have 
X_L to place over it the bladdered apparatus, 
b^ filled with oxygen, confining the gas 
below by a vegetable infusion, as that of 
cabbage or litmus, in a basin, d. The 
sulphur unites with the oxygen, and as 
it is consumed, the fluid rises in the jar, 
to e ; but at the same time the colour is 
15* 



I 



174 ELEMENTS OF CHEMISTRY. 

changed to red, shewing that an acid is formed. 
On analyizng the fluid, it has all the properties of 
weak sulphuric acid. 

Sulphuric acid, it has been mentioned, is a fluid 
of an oily consistence. It is usually of a brownish 
colour, but this is owing to impurities, for when 
pure, it is transparent and colourless. Its specific 
gravity is 1850, water being 1000. It has a very 
strong attraction for water, indeed it is never got free 
from it; even in its concentrated state, it contains 
about 20 per cent. When exposed to any gaseous 
fluid containing watery vapour, it very quickly 
attracts the moisture, and if exposed for some time, 
it will combine with so much, as to double its weight. 
During the union of the acid and water, there is a 
considerable rise of temperature, the greatest eleva- 
tion being produced by a mixture of about 3 by 
weight of acid, and 1 of water. When two meas- 
ures of the former and one of the latter are used, the 
mixture rises from 50 to 300. The evolution of heat 
is easily shewn in this instance. We have merely 
to mix them in the proportion stated, in a flask, and to 
give some idea of the heat produced, we may in- 
troduce into the mixture a small tube, with a little 
water, which very soon will be made to boil. {See 
Exp. 54.) This points out the necessity of being 
extremely cautious when mixing acid and water, lest 
the vessel should crack by the sudden heat. It ought 
always to be done in very thin ones, and they ought 
to be placed on a large plate. The specific gravity of 
the fluid differs according to the proportions, becom- 
ing greater as the acid is increased ; hence this affords 
us an easy method of finding the quantity of it in 
any mixture. See Appendix. 

By the application of heat to the mixture of acid 
and water, the greater part of the latter is expelled, 
and the former is left concentrated ; but, as has 
been already said, the whole cannot in this way be 
driven off. 



SULPHURIC ACID. 175 

Sulphuric acid is easily acted on by inflammables; 
perhaps the action with carbon is the most impor- 
tant. When any substance containing it^ as a piece 
of vegetable matter, cork for instance, is put into it, 
it acquires a dark colour, owing to its dissolving 
the carbonaceous matter. Hence the cause of the 
darkness of the acid commonly sold, a piece of cork, 
or some other vegetable matter, having fallen into 
the bottle. From this it maybe easily freed, and its 
transparency restored, by boiling it for a short time, 
by which the carbon is expelled, in the form of 
carbonic acid, taking oxygen from the sulphuric 
acid. 

Sulphuric acid is occasionally found pure. In some 
volcanic countries it issues in vapour from chinks in 
the ground, and being absorbed by the adjacent 
waters, gives the appearance of lakes of it. In its com- 
bined state, it is a very abundant production, united 
chiefly to the earths and metals. It is obtained in 
two ways, either by the combustion of sulphur mixed 
with nitre, or by expelling it from a substance in 
which it is in union with iron; the former is the 
method practised in this country, the latter on the 
continent of Europe. See Niire^ and Green Vit- 
riol or Sulphate of Iron, 

Sulphuric acid is applied to many useful purposes ; 
indeed, there is scarcely any substance more gene- 
rally used in the arts. It is employed by bleachers 
for scouring the cloth ; by dyers, for dissolving their 
indigo ; by calico-printers, for forming the sours in 
which they soak the cloth, previously to its immer- 
sion in the dye-stufl*; by brass-founders, button- 
makers, gilders, and japanners, for cleaning the sur- 
face of the metals with which they work ; and by hat- 
ters, tanners, paper-makers, and many others. It is 
used also in the preparation of nitrous and muriatic 
acid. 



176 ELEMENTS OF ClIEMISTRY. 



ALKALIES. 



The Alkalies are a class of substances having pro- 
perties by which they are distinguished from other 
bodies. They have been divided into two kinds, the 
fixed, which are potassa and soda, and the volatile^ 
which is ammonia ; the former so called, because 
they require an intense heat for their fusion and 
evaporation; the latter, because it is gaseous at a 
natural temperature. The alkalies are all soluble in 
water ; they have a disagreeable acrid taste, and are 
very corrosive. Their distinguishing character is 
that of changing vegetable blues to green. If, for 
instance, a few drops of the solution of any alkali 
be added to cabbage water, in a flask, the colour 
becomes green. If the infusion has been previously 
reddened by an acid, the addition of an alkali first 
restores the original colour, and then makes it green. 
Some of the colouring matters, as yellow turmeric, 
are changed to brown. It has been already men- 
tioned, that vegetable colours are used as tests of 
the presence of acids ; they are also employed for 
ascertaining whether a substance contains an alkali. 
They may be used either fluid, or spread on paper. 
On putting a piece of paper, besmeared with infu- 
sion of cabbage, into a fluid containing alkali, it 
becomes green ; or if turmeric paper be employed, 
it becomes brown. Another very delicate test of 
alkali is litmus, or archill, which is of a purplish 
colour, but becomes blue on the addition of an 
alkali. In using it, it is spread on paper, and put 
into the fluid ; and if the smallest quantity of alkali 
be present, it becomes blue. The alkalies have the 
property of uniting with acids, and forming a dis- 
tinct class of substances called compound, or neutral 
salts, because the qualities of the acid and alkali are 
destroyed, or neutralised. 



SODA. 177 



POTASSA. 



Polassa, sometimes also called Vegetable t^lkali, 
when pure, is commonly sold in small cylinders, but 
it is more frequently obtained in solution in water, 
in which state it is a transparent colourless fluid, of 
an oily consistence, having a disagreeable taste, and 
being very corrosive. In common with the alkalies, 
it changes the vegetable blues to green. 

When solid potassa is exposed to air, it absorbs 
moisture very rapidly by which it becomes liquid ; 
it also attracts carbonic acid, a minute quantity of 
which always exists in the atmosphere, so that its 
properties are quite changed. The same happens 
also with the solution ; hence the necessity of keep- 
ing them, but more particularly the former, in well 
stoppered phials ; indeed, it is necessary to have 
them secured by luting, to exclude the access of air. 

Potassa is no where presented by nature in its pure 
state. It exists, however, in considerable quantity 
in vegetables, in a state of combination, and from 
which it is always procured. For this purpose, the 
vegetable is burned in contact with air, and the 
ashes, by solution, afford the alkali, in union with 
carbonic acid. The carbonic acid is formed by the 
union of the carbon in the vegetable with the oxy- 
gen of the air, with which the potassa unites. From 
this compound the pure alkali is obtained. See Car- 
bonate of Potassa. 

Potassa is employed in bleaching, in soap-making, 
and in the manufacture of glass. See Lime^ Oil^ 
a n^ Silica. 

SODA. 

Soda, or the Mineral Mkali, resembles potassa in 
most of its properties. It is also procured in small 
cylinders, but generally in solution. It has a disa- 
greeable taste, and a strong attraction for water and 
carbonic acid, so that, if exposed to air for some 



178 ELLMENTS OF CHEMISTRY. 

time, its properties are completely altered. Lite 
potassa, also, it changes vegetable blues to green. 

Soda is usually procured by tlie combustion of sea 
weeds, and of plants growing near the sea; the pro- 
duct of the former is kelp^ of the latter barilla, which 
contain the alkali, in union with carbonic acid, and 
from which it is separated by lime. See Carbonate 
of Soda, 

It is employed for nearly the same purposes as 
potassa ; indeed, it is in general preferred, more 
particularly in the making of soap, as that formed 
by it is hard, whereas soap containing potassa is soft. 

The two alkalies now described were long con- 
sidered simple substances. Sir H. Davy has, how- 
ever, shewn that they are compounds, containing 
oxygen in union with metallic bodies, possessed of 
very remarkable properties. When potassa or soda 
is subjected to a very intense heat, along with iron 
filings, excluded at the same time from atmospheric 
air, the alkali is decomposed, its oxygen combines 
with the iron, and the other ingredient is disengag- 
ed ; it comes off in vapour, but as it is easily inflamed, 
it is necessary to have the end of the tube placed in 
oil ; the distilled oil of Petroleum, called Naptha^ 
is the best. On continuing the heat for some time, 
the metallic matter is given off, and is condensed in 
the oil. The metallic base of Potassa is called Po- 
tassium, that of Soda, Sodium. 

Potassium is the lightest known solid. When re- 
cently cut, it has all the appearance of lead. When 
exposed to air, it attracts oxygen very quickly, and 
is converted to potassa. Perhaps its most remarka- 
ble property is its taking fire the moment it comes in 
contact with water. If a small piece of it be thrown 
into a basin of water, it is kindled, and runs along 
the surface like a globule of melted metal, emitting 
a beautiful flame. Even though the water is frozen, 
the potassium is kindled the moment it touches it, 
as is beautifully illustrated by throwing a piece of it 



AMMONIA. 179 

into a cavity made in ice. In these cases the water 
is decomposed, it ^ives its oxygen to the potassium, 
and converts it to potassa. That an alkali is gene- 
rated by this means is easily shewn, by throwing a 
little potassium into a basin of 
'^^S / ^^bbage water, a^ which instantly 

V ^»— ^:^-— .., bgcQf^^^s green ; and if a funnel, 

b, be held over the potassium, a 

gas rises into it, which is inflammable. It is neces- 
sary, in this instance, to inclose the metal in a piece 
of wire gauze, and thrust it quickly by pincers under 
the fluid, otherwise it rolls along the surface, and the 
hydrogen escapes. 

Sodium has the same appearance as potassium, and 
very nearly the same properties ; it is not, however, 
kindled by water, but it decomposes it, taking its 
oxygen, by which it is converted to soda. 

AMMONIA. 

Ammonia, also called Hartshorn^ from its having 
at^one time been procured by the decomposition of 
harts' horns, is distinguished from the two others 
by its being gaseous at a natural temperature ; and 
hence, also, it is called volatile alkali. It is a trans- 
parent, colourless gas, having a pungent, irritating 
odour, and possessing a very strong attraction for 
water, which absorbs it with great avidity. The 
solution formed is transparent and colourless, having 
the peculiar odour of the gas, and, like the other 
alkalies, changing the vegetable blues to green. By 
the application of a slight heat to the fluid, the whole 
of the ammonia is expelled, and even by exposure to 
air the gas slowly escapes, so that it is necessary 
to keep it in well stoppered bottles. 

Ammonia is also a compound alkali ; it is com- 
posed of hydrogen and nitrogen ; and that it is so 
has been proved by numerous experiments. When 
electric sparks are passed through it, when in the 
gaseous form, it is decomposed, and hydrogen and 



180 



ELEMENTS OF CHEMISTRY. 



nitrogen gas are formed. By passing it also through 
a red hot earthen tube, it is decomposed, and an 
aeriform fluid is generated, which is a mixture of 
hydrogen and nitrogen. Thus, if a little hartshorn 
water be put into a retort, a^ attached to a tube, 





e 




C 




>^ 






V 




-^ 


^:^^^^^ 






^l «) 




* ■■ ^-. 


(^^^d 






i' 


M 






' i ■ ^ 



c, passed through a chauffer, 6, on applying heat to 
the retort, the ammonia is driven off, and, passing 
through the red hot tube, is decomposed, and its 
ingredients are collected in the jar, e. This cannot 
be ammonia gas, for this alkali is quickly absorbed 
by water. It is inflammable, and during its com- 
bustion generates water, and leaves nitrogen. It 
must therefore have been nitrogen and hydrogen, 
the latter of which has formed the water, by com- 
bining with the oxygen of the air. 

That ammonia is composed of hydrogen and nitro- 
gen, i^ also shewn by combining these gases, and 
hence the method of procuring the alkali. For this 
purpose, animal matter, as bones, horns, hoofs, pieces 
of skin, leather, &c. are subjected to heat in large 
retorts, which have receivers adapted to them, by 
which water and ammonia are given ofi", and collect- 
ed in the receiver. All animal matter contains four 
ingredients,— oxygen, hydrogen, carbon, and nitro- 
gen, and when exposed to heat, excluded from air, 
is decomposed. A part of the hydrogen and oxygen 
unite, to form water; part of the hydrogen and nitro- 
gen, by their union, lorm ammonia ; the remainder 
of the oxygen combines w^ith carbon to form carbonic 
acid, while carbon unites also with hydrogen to form 
carburetted hydrogen, which escapes in the form o* 



NEUTRAL SALTS. 



ISl 



gas. The water and the ammonia in union with the 
carbonic acid, are condensed in the receiver. 

Ammonia is not itself put to any particular use in 
the arts, but it is much employed in a state of com- 
bination, particularly with muriatic acid, in the well 
known salt called sal ammoniac. 



NEUTRAL SALTS. 




The Acids and Alkalies have a strong attraction for 
each other, and by their union they form a distinct 
class of compounds, called Neutral Salts^ because in 
them the properties of the acid and alkali are destroy- 
ed, or neutralised. That there is a change of pro- 
perties, that the compound no longer possesses the 
qualities of its ingredients, is easily shewn. The 
distinguishing character of an acid is its changing 
the vegetable blues to red, so that, if a 
few drops of any of them, say sulphtiric 
acid, is added to the colouring matter, «, 
it is reddened. The distinguishing feature 
of an alkali is its making the blue green ; 
hence, on adding a few drops of solution 
of soda to the same infusion, 6, it becomes 
green. As sulphuric acid will combine 
with soda, if we add the infusion a, or that 
containing acid, to 6, or that having the 
alkali, in a flask, a 6, they unite, and the 
original colour returns, shewing that the 
compound has no power of changing vege- 
table blues ; the properties of the acid 
and alkali have therefore been destroyed, 
hence the compound is said to be neutral. 
Neutral salts have properties common to all. 
They are soluble in water, though their 
solubility varies considerably, in diflerent instances. 
When obtained from their solutions by gradual cool- 
16 





182 ELEMENTS OF CHEMISTRT. 

ing, or by allowing the fluid to evaporate spontane- 
ously, they crystallize, the form of the crystals 
differing in different salts. The crystals in general 
contain a quantity of water, essential to their consti- 
tution, which in some instances amounts to half their 
weight; in others, however, it is but small. It is 
called water of crystallization. This difference in 
the proportion of water, gives to them particular 
qualities. Thus, when a moderate heat is applied 
to some of those having a large quantity of it, they 
at first liquefy, but on the continuance of the heat, 
become solid. Glauber^s salt, heated in a flask over 
a lamp, becomes quite limpid, like water, but after- 
wards forms a dry white cake. The fluidity in this 
instance is owing to the salt being dissolved in its 
water of crystallization, and hence it is called watery 
fusion, to distinguish it from fusion occasioned 
inerely by heat. Those salts, on the contrary, 
which have little water, crackle when heated, and 
the parts are separated, and thrown about. Sea salt 
thrown on a fire, or on a hot iron plate, has this 
effect. It is owing to the water in the salt being 
suddenly converted into vapour, the expansive force 
of which separates the particles with a crackling 
noise ; hence it is called crepitation, from the Latin 
word crepito, to crackle. Some of the neutral salts, 
when exposed to the atmosphere, absorb moisture, 
and become fluid. Thus, carbonate of potassa, or 
potashes, when strewed on a sheet of blotting paper, 
very soon exhibits signs of becoming moist. This 
is called deliquescence, from the Latin word deli" 
qiiesco, to become moist. Other salts, as carbonate 
of soda, or what is commonly called soda, when 
exposed to the air, lose their transparency, and 
acquire a white crust on their surface, and if left long 
enough exposed, fall into a white powder. This is 
owing to their losing their water of crystallization, 
which is taken away by the air. It is called efflor- 
escence^ from the Latin word efflorescOy to blow as a 



I^ITRATE OF POTASSA. 183 

flower. These changes point out the necessity of 
keeping the salts excluded from the atmosphere, 
which thus alters so much their properties. 

The names of the compound salts are formed of 
those of their ingredients, by which we are at once 
informed of the acid and alkali they contain. Thus, 
those having nitric acid are called nitrates^ those 
with muriatic acid muriates^ and those with sul- 
phuric acid sulphates^ to which the name of the 
alkali is attached, as nitrate of potassa, sulphate of 
^oda, muriate of ammonia. 

The neutral salts are a very interesting class of 
compounds, not only from their peculiar properties, 
but also from the uses to which they are applied in 
the arts. 

NITRATE OF POTASSA. 

Nitrate of Potassa^ called also Nitre^ or 5*^///- 
petre, is usually obtained in long crystals, which 
have a cooling but pungent taste. It is dissolved by 
about 7 parts of water at the temperature of 60, 
and at a boiling heat, it is soluble in about its own 
weight. The Avarm solution, on cooling, deposits 
crystals. During the solution of nitre in water, cold 
is generated, which is sometimes taken advantage 
of, as in procuring ice in India, the water being 
cooled by putting the vessels into a mixture of nitre 
and water, by which their temperature is very much 
reduced, and in this state it is exposed to the cool 
of the evening, in small cups, surrounded by straw 
and reeds. {See page 119.) 

Nitre acts very powerfully with inflammables, the 
action being peculiar, and attended with particular 
phenomena. When charcoal, or sulphur, is thrown 
into nitre, previously melted in a crucible, it burns 
with great splendour, accompanied occasionally with 
slight explosions. This is called deflagration. The 
rapidity of the combustion depends on the ease with 
which the nitre parts with its oxygen to the inflam- 



184 ]6lements or chemistry. 

mable ; of course, the product differs according to 
the substance with which it is mixed, but in all, the 
inflammable is converted into an acid, by its uniting 
with the oxygen of the nitric acid, which is thus 
destroyed, while the acid formed is left in com- 
bination with the potassa. Thus, when pieces of 
charcoal are thrown into melted nitre, the latter is 
converted into carbonate of potassa, the carbon com- 
bining with the oxygen of the nitric acid to form 
carbonic acid, which is left in union with the potassa, 
thus forming carbonate of potassa. When nitre is 
more intimately blended with the inflammables, the 
combustion is more rapid, and, if effected in a close 
vessel, is accompanied with explosion, the loudness 
of which depends on the quantity of the mixture,, 
and the vessel in which it is exploded. From this 
])roperty of nitre, it is employed in the preparation 
of signal lights and matches, and it is also one of the 
ingredients of gunpowder. 

The discoverer of gunpowder is not knowm. It 
is mentioned in the works of an author who wrote 
in the latter part of the 13th century, and it appears 
to have been used in the beginning of the 14th by 
EdW'Ard III. in his first attack against the Scots in 
1327. It was also employed at the siege of Calais 
in 1346. 

The materials used in the preparation of gun- 
powder are, nitre, charcoal, and sulphur, the propor- 
tions of w^hich vary in different places. In general, 
they are about 75 of nitre, 15 of sulphur, and 10 of 
charcoal. These must be all quite pure, otherwise 
the strength of the powder is diminished; accord- 
ingly, the nitre is always purified by solution and 
crystallization. For this purpose, it is dissolved in 
boiling water, and poured into large copper vessels, 
in which it deposits crystals. These are again dis- 
solved and crystallized, and even in some cases the 
process is repeated a third time, by which the whole 
©f the impurities are removed, and which impart to 



GtTNPOWDER. 185 

it deliquescent properties, or the power of absorbing 
moisture from air. After this, it is fused in iron 
pots, so as to drive off the water of crystallization. 
The sulphur employed in this process is generally 
that brought from Italy and Sicily. It is also purifi- 
ed, by fusing it, and allowing it to cool gradually, 
by which the earthy impurities fall to the bottom. 
From this, when solid, it is removed, and sometimes 
again submitted to a similar process. The charcoal 
is prepared by subjecting wood to a strong heat 
in cast iron cylinders, in which it remains till it 
becomes cold, and it is in general kept in boxes till 
required. The lighter woods are generally prefer- 
red, such as alder and dogwood, and they are always 
freed of the bark before being charred. 

The ingredients are first ground to powder sepa- 
rately, and then mixed in the proportions mentioned, 
after which they are more intimately blended, by 
means of iron rollers, the mixture being kept con- 
stantly moist, to prevent explosion, and the quantity 
not exceeding about 50 pounds under each roller. 
The apartment in which this process is performed is 
constructed of wood work, that, should an explosion 
occur, the consequence may be as little as possible. 
After the materials are properly incorporated, the 
mixture is subjected to the process of corning^ by 
which it is reduced to small grains. This is done 
by pressing the paste into small pieces, which are 
placed in circular boxes, with parchment bottoms, 
perforated with holes of different sizes, according to 
the required size of the grains, and in w^hich, also, 
there is a block of hard wood. These are connected 
with a wheel, by which they are moved in a hori- 
zontal direction, and, by the action of the block, the 
paste is reduced to grains, and passes through into 
boxes placed beneath for their reception. After this 
they are glazed^ by putting them into barrels, 
revolved by machinery, in which, by the constant 
friction against each other, their surface is harden^ 
16* 



186 ELEMENTS OF CHEMISTRY. 

ed, and they acquire a fine gloss, which, though it 
diminishes a little the strength of the powder, yet 
renders it less liable to be injured by moisture. The 
next part of the process is the dryings which is done 
in different ways in different manufactories. In 
general, the powder is placed on shelves, in a small 
brick house, through which there passes the vent of 
a furnace, or into which a red hot cylinder of iron 
projects, and which is kept constantly hot by a fire 
without the building. A method of drying gunpow- 
der by steam has been lately practised, in which 
there is no danger whatever, as the temperature in 
this way cannot go beyond 212, {See page 82.); but 
it is said not to dry it so uniformly as the other, and 
is therefore not much practised. It consists merely 
in placing the powder on boxes, kept constantly full 
of steam, the condensed vapour escaping from the 
box, by a tube terminating without the building. 
After the whole of the moisture is expelled, the 
powder is put into casks, keeping it as much as pos- 
sible excluded from the air, particularly if moist, for 
when much exposed, it absorbs moisture; and as the 
nitre is the only soluble ingredient, a part of it is 
thus apt to be removed, by which the powder is 
destroyed. 

In the preparation of gunpowder, the more mi- 
nutely the materials are ground, and the more 
intimately they are mixed, the greater is the explo- 
sive power of the powder. The strength also de- 
pends in a great measure on the drying; for when 
too much heat has been applied, part of the sulphur 
is driven off; besides, a hard crust is formed on the 
surface, which prevents the moisture escaping from 
the inner parts. When well prepared, the powder, 
when exploded on a piece of paper, ought to leave 
little or no residuum, the whole of the ingredients 
entering into a new state of combination, and gene- 
rating products, which are given off in the form of 
gas. If any particles remaio on the paper^ it shewi^^ 



GUNPOWDER. 187 

either that the ingredients have not been pure, or 
not in proper proportion. When gunpowder is 
heated, the action is owing to the ease WMth which 
the nitre parts with oxygen to the inflammables, the 
sulphur and carbon combining with it to form gase- 
ous products, and the acid of the nitre, by losing 
part of its oxygen, forms also a gaseous substance, 
the generation of all of which is the cause of the 
explosion- That a large quantity of aeriform matter 
is given oflf by gunpowder, is easily shew^n, by put- 
ting a little of it moistened into a tube, kindling it, 
and then plunging it quickly under the mouth of a 
jar, inverted on a water trough, keeping the mouth 
of the tube down. As the powder is moistened, it 
does not explode ; it is slowly consumed, and gas 
arises into the jar. This, when cold, occupies about 
250 times the volume of the powder itself; but the 
heat evolved during the action expands it greatly, so 
much so, that it is supposed to be about 1000 times 
the volume ; and as it exerts the same pressure as 
the atmosphere, 15 pounds on the square inch, we 
have thus the pressure of 1000 atmospheres, so that 
its expansive force is 15,000 pounds, by which a 
ball is propelled from a gun with a velocity of about 
2000 feet in a second The strength of different 
kinds of powder varies, however, considerably, and 
hence it is that each sample is tried before it is 
purchased by government, which is done by trying 
the distance to which it sends a ball, using the same 
gun, and similar balls, and the same weight of pow- 
der, in all the trials. 

Nitrate of potassa is also employed in the prepara- 
tion of signal lights and matches. The portfire of 
artillerymen is a mixture of 60 of nitre, 40 of sul- 
phur, and 20 of gunpowder. The materials are 
made into a paste, and stuffed into cylinders of paper. 
Signal lights are mixtures of nitre and sulphur, with 
a little metallic matter, that communicates to the 
flame a particular colour. The white light is com- 



188 



:blements of chemistry. 



posed of 6 of nitre and 2 of sulphur, io which is 
added 1 of orpiment, or yellow arsenic. The blue 
light contains the same proportion of nitrate and 
sulphur, with two of crude antimony. 

The action with nitrate of potassa and sulphuric 
acid is important, as by it we are enabled to decom- 
pose the nitre, and procure its acid, or rather nitrous 
acid, which is the one always employed in the arts, the 
sulphuric acid, by its stronger affinity, decomposing 
the nitre, and combining with its potassa. For this 
purpose, 3 lbs. of nitre are put into a glass retort. A, 
and 2 lbs. of sulphuric acid are poured on it. After 
being properly mixed, heat is applied, and a receiver, 




B, adapted, which must be kept cold by a stream of 
water from the funnel, C, which has a grooved cork 
put into its throat, the neck of the retort being but 
loosely fixed to the mouth of the receiver. The 
heat must be continued as long as acid fumes come 
off, and the fire after this extinguished, and the 
retort allowed to cool gradually, to prevent it from 
cracking. What remains in it is the compound 
formed by the union of the sulphuric acid and the 
potassa of the nitre. It is but sparingly soluble, and 
requires to have warm water poured on it repeatedly, 
and left on it several days each time, so as to wash 
it out. The colour of the acid procured depends in 
^ great measure on the heat ; if it has been high, it 



USES OP JflTRE. 1S9 

is dark coloured. By using a larger proportion of 
sulphuric acid, as equal weights, less heat is requir- 
ed, so that the acid is much paler. 

Nitre is used also for affording nitrous acid vapour, 
for purifying apartments in which the sick have been 
confined, or for preventing contagion. For this pur- 
pose, a little oil of vitriol is placed in a tea-cup, 
which is to be heated in a ladle with sand, taking 
care not to heat it so much as to make it give off 
fumes. Some nitre is then to be thrown in, by which 
the sulphuric acid unites with the potassa, and the 
nitrous acid vapour is disengaged. If the room is 
large, several cups may be placed in different parts 
of it, or the ladle may be carried from one part to 
another. 

Nitre is employed also in the preparation of sul- 
phuric acid, the method always practised in this 
country. When sulphur burns slowly in air, a sub- 
stance called sulphurous acid, but better known by 
the name of fumes of sulphur, is formed ; but when 
it is mixed with a little nitre, the combustion is more 
lively, and sulphuric acid is the product. To obtain 
the acid from this mixture, large leaden chambers 
are built, having two openings, one a door at a few 
inches from the bottom, for the introduction of the 
mixture, the other, also near the bottom, furnished 
with a stop-cock, through which the acid is drawn 
off. "Water is poured in to the depth of about two or 
three inches, and the mixture of sulphur and nitre, 
in the proportion of about 8 or 10 of the former to 1 
of the latter, contained in an earthen pot, is placed 
on a stand in the chamber, and then kindled. When 
the combustion has ceased, more is put in, and in 
this way it is carried on for some weeks, at the end 
of which the fluid is drawn off into large retorts of 
glass or platinum, in which it is concentrated by 
evaporation, till it becomes of the proper strength, — 
specific gravity 1850. It is then poured into 
large green glass bottles, called carboys^ surrounded 



190 ELEMENTS OF CHEMISTRY. 

by basket-work, in which state it is sent to mar- 
ket. 

Sulphuric acid prepared in this way always con- 
tains a little lead, derived from its aclin^; on the walls 
of the chambers, but from which it is easily freed by 
mixing it with an equal quantity of w^ater, by which 
a w^hite powder falls as the mixture becomes cold. 
This is the lead, in union with a little of the acid, 
from which the clear fluid is poured oflf, and, if re- 
quired strong, must be concentrated by evapora- 
tion. 

The use of the nitre in this process, is to enable 
the sulphur to get a sufficient supply of oxygen, to 
convert it entirely into sulphuric acid. When the 
sulphur is inflamed, it forms sulphurous acid, by 
taking oxygen from the air, and from the acid of the 
nitre, by which a gas is formed that has the power 
of depriving the atmosphere of its oxygen, and 
communicating it to the sulphurous acid, to convert 
it into sulphuric acid, so that each portion of sulphu- 
rous acid formed acquires a sufficient quantity of 
oxygen indirectly from the air, through the medium 
of the substance set free from the acid of the nitre. 
Here there is no necessity for a great quantity of 
nitre, because the gas generated from it, and which 
takes the oxygen from the air, is brought back again 
to the same state as before, and is again ready to take 
more oxygen^ and give it to the next portion of the 
acid. 

Nitre is furnished by nature nearly in a state of 
purity. It exists in considerable quantity in the soil 
of America, China, and India, from which it is 
obtained merely by solution, filtration, and evapo- 
ration to dryness, afibrding what is called rough ni- 
tre^ and which is afterwards purified by again dissolve 
ing it, and crystallizing. 

Nitre was at one time also procured, particularly 
in France during the late war, by mixing chalk, or 
old mortar^ with animal matter undergoing putre^ 



CARBONATE OP POTASSA. 



191 



faction; but this process is not now practised, the 
supply from the quarters mentioned being suflScient. 



CARBONATE OF POTASSA. 

Carbonate of Potassa, as its name shews, is a 
compound of acid and potassa. It is better known 
by the name oi Potashes, Pearlashes, and Salt of 
Tartar. It is generally in ir eiularly formed 
masses^ having a disagreeable acrid laste, similar to 
that of the pure alkali, but not so corrosive. When 
exposed to the atmosphere, it very quickly absorbs 
moisture, and becomes fluid ; it therefore deliques- 
ces. Hence the necessity of keeping it excluded 
from the air. It is very soluble in water, requiring 
not more than its own weight to dissolve it. The 
solution is transparent and colourless, and possesses 
the property of changing the vegetable blues to green. 
It has been already mentioned, in the remarks 
made on salts in general, 'that the acids and alkalies 
combine, and form compounds, in which the prop- 
erties of both are destroyed. This, however, is not 
always the case ; in some instances the compound 
has an excess of acid, and has therefore acid proper- 
ties, while in others there is a superabundance of 
alkali, and, of course, alkaline properties, of which 
the carbonate of potassa is an example, the solution 
changing the blues to green, shewing that there is 
an excess of alkali. 

When an acid is added to carbonate of potassa, it 
is decomposed ; it combines with its alkali, and dis- 
engages the carbonic acid. Thus, if the salt be put 

into a retort, a, 
and oil of vitriol 
be poured on it, 
an elastic fluid is 
instantly disenga- 
ged, and may be 
collected in the 
jar b ; on plung- 




192 ELEMENTS OP CHEMISTRY. 

ing a lighted taper into this, it is instantly extin- 
guished. Hence the decomposition is effected by 
the stronger force of the attraction of the sulphuric 
acid for the potassa, by which it unites with it, 
and the carbonic acid passes off in the form of gas. 

Carbonate of potassa is prepared by the combus- 
tion of vegetables, more particularly in those coun- 
tries which abound in wood, as in America and Rus- 
sia. For this purpose, the ashes collected from the 
wood used as fuel are washed with water, and the 
solution, after filtration, evaporated to dryness. 
What is left is the carbonate, though in an impure 
state, as it contains vegetable matter, and some other 
salts ; but it is sufficiently pure for the uses to which 
it is generally applied. 

Vegetables always contain potassa in some state of 
combination ; hence, by the combustion^ the carbon 
in them combines with the oxygen of the air, andr 
forms carbonic acid, which unites with the potassa, 
and thus forms a carbonate. Different vegetables 
yield different quantities of potassa ; hence the dif- 
ferent kinds of potashes contain different quantities 
of pure potassa. It is of the utmost importance, 
therefore, that we should have an easy method of 
ascertaining the actual quantity they contain. See 
Jippendix, 

Carbonate of potassa is employed in bleaching, 
and in the manufacture of glass and soap. It is 
used also for yielding potassa, by depriving it of its 
carbonic acid. See Lime. 

CARBONATE OF SODA. 

This Salt, though commonly called Soda, is alto- 
gether different from the alkali of the same name. 
Its other title shews, that it is a compound of soda 
and carbonic acid. It is usually sold in irregularly 
formed crystals, which have an acrid taste, and are 
very soluble^ requiring only about two of w^ater at a 



CARBONATE OF SODA. 193 

natural temperature, and less than their own weight 
at a boiling heat, to dissolve them. The solution is 
transparent and colourless, and changes the vegetable 
blues to green ; hence it must contain an excess of 
alkali, that is, the carbonic acid in it is not saturated. 
When exposed to the air, it effloresces ; it loses its 
water of crystallization, and becomes a dry white 
powder. In this respect it differs from the former 
salt, which is very deliquescent. It resembles it, 
however, in its action with acids. If any of these 
be added to it, it unites with the soda, and the car- 
bonic acid is disengaged, so that, if the same appar- 
atus be used as for carbonate of potassa, the gaseous 
acid may be collected* 

Carbonate of soda is generally procured by the 
combustion of sea-weeds, and plants growing near 
the sea; the produce oi the former is called help^ of 
the latter barilla. Barilla is made principally along 
the shores of the Mediterranean, by burning differ- 
ent kinds of plants that grow near the sea. For this 
purpose, they are collected in Autumn, and laid on 
the ground to dry. Holes, each capable of holding 
about a ton, are dug in the earth, and over these are 
placed bars of iron, on which the plants, mixed with 
straw or reeds, are burned, portions of the mixture 
being thrown in, w^hen the former is nearly consum- 
ed. During the combustion, the materials undergo a 
sort of fusion, in which state they are w^ell stirred ; and 
when the pits are full, they are covered w^ith earth, 
till the product cools, after which it is removed, and 
broken to pieces. 

Kelp is prepared nearly in the same way, from 
the different sea-weeds, which are cut in June and 
July, and exposed on the rocks till thej^ become dry, 
care being taken to keep them from rain. They are 
then burned, either in pits dug in the sand, or on the 
surface of the ground, surrounded by stones, a fire 
being previously kindled, to promote the combus- 
tion. When a considerable quantity of the ashes is 
17 



194 ELEMENTS OF CHEMISTRY. 

collected, the heat is sufficient to fuse them, after 
which they are well stirred ; and in this way the 
process is carried on for several days. The product 
is then covered till it becomes cold, and afterwards 
broken to pieces. 

Kelp and barilla contain a number of substances, 
as lime, magnesia, sea sand, charcoal, and different 
salts, the principal of which is carbonate of soda, 
the former having from 3 to 6, and sometimes 8 per 
cent, the latter having from 12 to 15, and occasion- 
ally, though rarely, about 17 per cent. This is de- 
rived from the decomposition of the sea salt which 
the plants contain, the carbonic acid being formed 
by the combustion of the carbonaceous matter. 
Kelp and barilla are used for yielding carbonate of 
soda. For this purpose, they must be dissolved in 
boiling water, the solution filtered, and evaporated to 
dryness. The residuum must be again dissolved, 
and the fluid slowly evaporated, to allow the impu- 
rities to be deposited. After these are removed, the 
evaporation is continued, and carbonate of soda is 
procured. 

Kelp and barilla are used, in their entire state, for 
soap-making, and in the manufacture of glass ; in 
the former, owing to the soda they contain ; in the 
latter, owing partly to it, partly to other substances, 
which are necessary ingredients in some kinds of 
glass. See Soap and Glass, 

As the diflerent kinds of kelp and barilla afford 
different quantities of soda, it is of importance to be 
able to ascertain the quantity, as on this depends 
their value. See Appendix. 

Carbonate of Soda is employed in bleaching, soap- 
making, and glass-making, and it is used also in 
washing ; the alkali acting on the greasy matter in 
the cloth, and forming with it a kind of soap. It is 
used also to yield pure soda, by depriving it of its 
carbonic acid. See Lime, 



MURIATE OF SODA. 195 



MURIATE OF SODA. 



This salt, a compound of muriatic acid and soda, 
is the well known substance sea salt. It is gene- 
rally in small crystals, the form of Avhich varies ac- 
cording to the method of preparing it. When quite 
pure, it is not altered by exposure to the atmosphere, 
but the salt in common use deliquesces, owing to im- 
purities. It is soluble in about two and a half of 
cold water, and, what is very remarkable, it requires 
as much when boiling, at least, if there is any differ- 
ence, it is very trifling ; accordingly we cannot pro- 
cure crystals by cooling a w^arm solution ; they are 
obtained by driving off the water by evaporation. 

When sea salt is mixed with ice or snow, there is 
a considerable reduction of temperature, the salt 
acting on the ice, by which both become fluid, 
{See page 118.) The most important action of the 
acids with muriate of soda, is that with sulphuric, 
by which we are enabled to decompose it, and thus 
procure muriatic acid. For this purpose equal weights 
of salt, acid, and water, are used. The salt is put 
into a retort, A, {See page ISS^) and the acid, previ- 
ously diluted with a third of the water, and allowed 
to cool, is poured on it. The remainder of the wa- 
ter is put into the receiver, B, heat is applied through 
the medium of a sand bath, and in about half an 
hour, the receiver must be luted to the retort, by 
means of pipe clay, and kept cold by a stream of 
water, C, and the heat continued as long as any acid 
comes off. In this instance, the sulphuric acid unites 
with the soda, while the muriatic acid is disengaged ; 
it comes off in the form of gas, bringing along with 
it the v/ater of the other acid, and is condensed by 
the fluid in the receiver. If the sea salt is pure, the 
muriatic acid is colourless ; but it is generally of a 
pale brownish colour, owing to impurities, which, 
however, is of little consequence for the purposes to 
which it is commonly applied. 



196 ELEMENTS OF CHEMISTRY. 

It was formerly mentioned, that muriatic acid is 
employed for purifying apartments, and for prevent- 
ing contagion. It is owing to the ease with which 
sea salt gives off its acid, that it is used for this 
purpose. The process is a very simple one : Into 
a tea cup or saucer, heated by holding it near a fire, 
a little sea-salt is put, and on it is poured about an 
equal quantity of oil of vitriol ; which instantly 
unites with the soda, and disengages the muriatic 
acid. Should the apartment be large, it is necessary 
to have several vessels ; and in this instance, it is 
best to employ soup plates, and place them on warm 
bricks. 

Sea salt is perhaps one of the most abundant pro- 
ductions of i^ature; it is the principal ingredient in 
the saline matter procured by the evaporation of sea 
water, which contains about 3 per cent, of saline 
matter, fihs of which are muriate of soda. It is 
likewise found in immense quantity in the bowels of 
the earth, as in the mines of Cheshire, and Poland ; 
and in some countries there are mountains almost 
entirely composed of it, a remiarkable instance of 
which is in Cordova in Spain. When obtained from 
sea water, it is called sea salt, when got from other 
sources, it is termed 7'ock salt. For procuring it 
from sea water, different processes are followed, 
according to the temperature of the place. It is 
well known, that when water, holding a salt in solu- 
tion, is frozen, it deposits the whole of the salt; 
thus, the ice found in the polar regions, when melt- 
ed, affords pure water. In cold countries, advantage 
is taken of this. The sea water is received into 
large shallow pits, in which most of it is frozen, and 
deposits the salt, so that the fluid beneath contains 
a much greater quantity than before. The ice is 
therefore broken, and the fluid evaporated by which 
its salt is obtained. In warm climates, sea water is 
likewise collected in pits, which communicate with 
each other. When that in the first is made suffi- 



MURIATE OP SODA. 197 

ciently strong by spontaneous evaporation, it is 
drawn into the second, and so on successively, till it 
arrives at the last, in which it is nearly a saturated 
solution ; of course, by farther evaporation, the salt 
is deposited. In this country, sea salt is obtained 
both by artificial, and spontaneous evaporation. For 
this purpose, the water is received into a large reser- 
%'oir, from which it is constantly evaporating, and 
after this, is pumped into shallow pans, under which 
a strong fire is applied. As the fluid is evaporated, 
the salt is gradually formed on the surface, and falls 
to the bottom, from which it is raked out, and put 
into baskets to drain. The saline matter obtained by 
these diflerent processes, is not pure muriate of soda ; 
it contains other salts, which give it a disagreeable 
taste, and render it unfit for many purposes, for 
which, when pure, it is so much prized; different me- 
thods have therefore been followed for purifying it, 
the principal of which is that recommended by Lord 
Dundonald, founded on the fact, that it is not more 
soluble in boiling than in cold water, while the re- 
verse is the case with the other substances with which 
it is mixed. A saturated solution of the saline mat- 
ter is made at a natural temperature, and after being 
brought to a boiling heat, is poured on another por- 
tion of salt, placed in a conical vessel, with the point 
down, and having a small opening in it. As the im- 
purities are more soluble in warm than in cold water, 
more of them are dissolved, but there is no action on 
the muriate of soda, so that, by repeated washings 
in this way, nearly the whole of them is removed. 
Still, however, the salt is not quite pure, and hence 
the preference given to rock salt, at least for 
certain purposes, as it contains so little of the for- 
eign ingredients, indeed, in some places, it is almost 
pure. When rock salt is not pure, after being bruis- 
ed, it is dissolved, and the solution filtered and 
evaporated, by which muriate of soda is pro- 
cured. 

17« 



19S ELEMENTS OF CHEMISTRY. 

Sea salt, besides its use as a seasoning to food, is 
employed largely in the arts. Its use in generating 
cold, and in preparing muriatic acid, have been 
already described. From its power of preventing 
putrefaction, it is used in preserving meat, fish, and 
butter. It is employed in the manufacture of potte- 
ry, for giving a glazing to some kinds of earthen 
ware, and in the making of glass and soap, to the 
latter of which it imparts hardness. 

Perhaps the most important process carried on 
with it is decomposing it, to make it yield soda. 
This was at one time carried on by the addition of 
litharge, a compound of oxygen and lead, Vv^hich 
unites with the muriatic acid, and sets the soda free; 
but it has been abandoned as unprofitable. The only- 
method now followed, is to decompose it by sulphu- 
ric acid, which combines with the soda, and forms 
sulphate of soda, and afterwards to decompose the 
sulphate. The residuum of the process for prepar- 
ing muriatic acid, is a compound of soda and sulphu- 
ric acid, the sea salt being, as has been already ex- 
plained, decomposed by the sulphuric acid, and it is 
it that is used for preparing soda. For this purpose, 
it is mixed with charcoal and chalk, or lime, and sub- 
jected to a strong heat for some hours, by which the 
sulphuric acid is destroyed, the charcoal uniting 
with its oxygen to form carbonic acid, which is left 
combined with the soda, so that, by dissolving the 
product, filtering, and evaporating, crystals of car- 
bonate of soda are obtained. They are not, however, 
pure, but they are suflSciently so for most of the 
purposes to which they are applied. It is in this 
way that a great deal of the soda now used by soap- 
makers and bleachers is prepared. 

MURIATE OF AMMONIA. 

Muriate of Ammantay commonly, called Sal 
JimmoniaCy which, as the name shows, is a com- 
pound jof muriatic acid and ammonia, has been long 



MURIATE OF AMMONIA. 199 

known and in use in the arts. As generally obtain- 
ed, it is in large cakes of a semicircular form, owing 
to the figure of the vessel in which it is prepared. 
It is very tough, and reduced to powder with great 
diflSculty. It requires rather more than three parts 
of cold, and about its own weight of boiling water, 
to dissolve it, and during solution, generates cold. 
When exposed to heat, it sublimes, or rises in 
vapour, and is again condensed, unchanged in its pro- 
perties, on the cool part of the apparatus. When 
exposed to the atmosphere it becomes moist. It is 
easily decomposed by acids, but the only action of 
any importance is that wath nitrous acid, by which 
an impure aqua regia is formed, and which is much 
employed in the arts. It is prepared by putting 3 
parts of the powder of the salt into 1 of acid, in a 
flask, and applying a very slight heat, till the whole 
is dissolved. In this ease part of the nitrous acid 
unites with the ammonia, and sets free muriatic acid, 
which acts on the rest of the other acid, as when 
the pure acids are used, {see page 173) \ so that the 
only difference in the product is its containing, be- 
sides aqua regia, a little of the compound formed by 
the union of the ammonia and nitrous acid, but which 
is not at all injurious in the processes in which it is 
used. 

It has been already mentioned, that sal ammoniac 
generates cold during solution in water ; if it be 
mixed with an equal quantity of nitre, both reduced 
to powder, and be dissolved, the cold becomes still 
more intense. The proper proportions are 4 of the 
mixture to 5 of water. As a proof of the cold, 
we have merely to put into the solution a tube with 
v>rater, which will be very soon frozen. Here there 
is no waste of the materials, because the product, 
w^hich is merely a solution of the salts, may be 
procured by boiling to dryness, and will, after being 
powdered, answer for the same purpose. Being 
therefore economical, when ice cannot be procured^ 



a 



200 ELEMENTS OF CHEMISTRY, 

it is much employed for keeping cool receivers into 
which vapours are to be condensed, during distilla- 
tion, and for other purposes of a similar nature. 

Sal ammoniac was first procured from the dung of 
animals, a process long carried on in Egypt. It is 
now, however, prepared by the decomposition of 
substances containing its ingredients. The process 
so long carried on in Edinburgh by the late Dr 
Hutton, consisted in adding oil of vitriol to soot, 
filtering the mixture, and evaporating to dryness. 
The residuum was then mixed with sea salt, subjected 
to heat in a close vessel, a, to which a top, d, ^ — s. 
was adapted, and into which sal ammoniac ( ^ J 

was sublimed and condensed. Coal, when |i C 

burned, yields a considerable quantity of 
ammonia formed by the union of hydrogen 
and nitrogen, which exist in it, so that, when 
sulphuric acid is mixed with soot, it combines 
with the ammonia. When this compound is mixed 
with muriate of soda, and heated, there is a double 
decomposition, or an exchange of ingredients; the 
sulphuric acid combines with the soda, and the muri- 
atic acid with the ammonia, by which two new 
compounds are formed, sulphate of soda, and muri- 
ate of ammonia; the latter of which is sublimed into 
the top, hj the former is left in the lower vessel, «, 
so that by this process two useful products are pro- 
cured, sal ammoniac, and sulphate of soda, or Glau- 
ber's salt. 

Another method of preparing sal ammoniac, and 
one which is now ver}^ much practised, is decompos- 
ing the ammoniacal fluid given off from coal, during 
the preparation of coal gas, and which is collected in 
a particular part of the apparatus, destined for the 
purpose. This is mixed with sulphuric acid, and 
treated with sea salt as already described. In some 
places, the ammonia is procured by decomposing 
animal matter, and then treating it in the same way. 
Instead of sea salt, some manufacturers use what is 



CHLORATE OF POTASSA. 201 

called the hittern of sea water : that is, the fluid 
from which the sea salt has been extracted, and which 
contains muriatic acid in union with magnesia. It 
is evaporated to dryness, and mixed with the com- 
pound of sulphuric acid and ammonia. Here, of 
course, a similar change takes place ; the sulphuric 
acid uniting with the magnesia, and the muriatic 
with the ammonia, so that the products are sal am- 
moniac, and sulphate of magnesia, or Epsom salts ; 
and hence the method by which the latter is gene- 
rally prepared. 

Sal Ammoniac is employed abundantly in the arts. 
Its use in preparing aqua regia, and for generating 
cold, has been already noticed. It is used in solder- 
ing some of the metals, and in tinning iron and 
copper, a layer of the salt being put on the metals, 
to prevent the action of the air at the temperature 
to which they are subjected. It is used also by 
dyers in preparing some of their dyes, and it is de- 
composed so as to make it yield its alkali. See Lime* 

CHLORATE OF POTASSA. 

The salt commonly sold under this name, is usually 
in small thin crystals, requiring about 16 parts of 
cold water to dissolve them. When subjected to 
heat, they give off a large quantity of oxygen gas, 
showing that they contain it as one of their ingredi- 
ents. Its action with the inflamm.ables is, however, 
the most interesting, with some of which it acts 
wdth great violence. When phosphorus is mixed 
with it, and the mixture, wrapped in tin foil, is 
struck with a hammer, it explodes with great force, 
rendering the experiment dangerous, and it ought 
not to be performed on more than a quarter of a grain. 
Charcoal in powder also acts in the same way, and 
the same is the case with sulphur; indeed, the mix- 
ture with it explodes by friction. If equal parts of 
the powder of the salt, and flowers of sulphur be 
rubbed in a mortar, they explode with great violence. 



203 ELEMENTS OF CHEMISTRY. 

This shews the necessity of operating on small quan- 
tities, and in making the mixtures, the materials 
ought to be reduced to powder separately^ and 
mixed on paper by means of a piece of wood. These 
actions are supposed to be owing to the ease with 
which the salt parts with oxygen to the inflam- 
mable, the friction or percussion favouring the action, 
probably by the generation of a little heat. The 
acids act also very easily with this salt. The action 
with sulphuric acid is important, as by it a gaseous 
matter is disengaged, which sets fire to the inflam- 
mable matter. The experiment is, however, a 
dangerous one, unless performed on very minute 
quantities, or some means be taken to prevent the 
action from going on too rapidly. The safest method 
of shewing the action, is to put at the bottom ^ 
of a glass of water, a, about 10 grains of 
the salt, with some chips of phosphorus, and 
then pour in, through a long funnel, A, a 
few drops of sulphuric acid, which, by its 
weight, falls, and comes in contact with 
the salt, without mixing with the water. 
The moment it does this, it acts on it, 
setting free a gas, which inflames the phos- 
phorus. 

From the great explosive powder of this salt, when 
acted on by inflammables, it was proposed to use it, 
instead of nitre, in the preparation of gunpowder ; 
indeed, an attempt was made in France to employ 
it for this purpose; but as soon as the mixture was 
rubbed, it exploded, and proved fatal to some of the 
workmen, so that the process was abandoned. But, 
besides the danger, the expense of preparing it pre- 
cludes its use. It has, however, been recommended 
by Mr Forsyth, and is in general use, as a priming 
for his patent firelock, now known by the name of 
percussion lock. In the locks first used, the priming 
was kept in a reservoir attached to them, but ex- 
plosions sometimes happened ; accordingly, various 





USES OP CHLORATE OP POTASSA. 203 

improvements have been made on it. That now in 
common use^ and which is not only the simplest, but 
the safest, consists merely of a 
small hammer, a, fixed to the 
trigger, and terminated by a 
little cup at 6, which fits the 
projection, <?, in which is the 
touch-hole, communicating WMth 
the barrel. A number of small 
copper caps, fif, are made to fit accurately the projec- 
tion, c, and into these is placed a little of the explo- 
sive mixture. After the barrel is loaded, a cap is 
put on, and the hammer brought down cautiously on 
it. When the piece is to be discharged, the hammer 
is brought to full cock, and by drawing the trigger, 
it comes down with a smart blow on the cap, and 
explodes the mixture, the flame from which rushes 
through the touch-hole, and sets fire to the powder. 
This lock is attended with several advantages. 
There is no danger of the priming being injured by 
moisture, by which the common locks so frequently 
hang fire ^ and indeed often cannot be used during 
wet weather. There is also less likelihood of any 
accident happening, the lock being much less likely 
to be cocked by any means, as by passing through a 
hedge, than the common one. Difierent mixtures 
have been used. That recommended by Forsyth, was 
the salt with sulphur and charcoal ; but the substance 
commonly called crude antimony and which is a 
compound of the metal antimony and sulphur, is 
generally employed, being mixed w^ith about an 
equal quantity of the salt. 

This salt is likewise employed as a means of pro- 
curing a light. The action with sulphuric acid and 
inflammable matter, has been already noticed. It is 
in this way that a light is obtained. After being 
reduced to powder, it is mixed on a piece of paper, 
'with an equal bulk of the powder of white sugar, 
and made into a thick paste, with mucilage, or it 



204 ELEMENTS OP CHEMISTRY. 

may be mixed with flour, and made into a paste with 
water, in which state it is put on the end of a small 
sulphur match, taking care to leave some of the 
sulphur uncovered. When this is dipt into oil of 
vitriol, there is an action similar to that already 
described with phosphorus, by which the sugar is 
inflamed, and kindles the sulphur match. These 
matches are in general put into a box, with a small 
bottle of acid, and a wax taper. Tiiey must be kept 
dry, and the acid ought to be frequently renewed, as 
it is apt to absorb moisture, particularly if the stop- 
per has been frequently removed. 

By this action, pieces of artillery may also be dis- 
charged. For if a small pipe, filled with the mixture, 
be placed in the touch-hole, on patting on a drop of 
acid, it is kindled, and the flame rushes into the 
barrel. 



EARTHS. 

The greatest part of this globe consists of the 
earths. They are therefore of peculiar interest, not 
only from their abundance, but from their use in the 
arts. When we take a superficial view of the fossils 
composing this globe, we perceive an immense vari- 
ety in them ; but when we examine them chemically ^ 
we find that this diversity is occasioned by the com- 
bination of a few bodies. The earths do not exceed 
nine in number, and of these, three are very rarely 
found ; so that, by the union of six, almost all stony 
substances are produced, and of these only four are 
used in the arts— lime, magnesia, alumina, and silica. 

The earths in general are dry and brittle, of a 
whitish colour, without smell, and usually also without 
taste. They are not inflammable, and their specific 
gravity never exceeds 4.5, compared to water as 1. 
Some of them are sparingly soluble, while others 
cannot be dissolved by water. 



LIME. 205 



LIME. 



Lime, when pure, is a white, brittle, and mode- 
rately hard substance, having a peculiar feel, and a 
hot acrid taste; it is very corrosive of animal and 
vegetable matter. When exposed to the most intense 
heat of a furnace, or to the rays of the sun, concen- 
trated by a powerful lens, it is not fused ; it may, 
however, be melted by the oxy-hydrogen blow-pipe, 
that is, by the heat generated by the combustion of 
hydrogen, animated by a stream of oxygen. It has 
a very powerful attraction for water, absorbing it 
quickly from any other substance ; it is, however, 
but sparingly soluble. The action between water 
and lime is peculiar. When poured on it, it is 
absorbed with a hissing noise; the lime becomes 
warm, it cracks, and falls into a dry white powder, 
and at the same time watery vapour is given off. 
This process is called slaking^ and the product is 
called slaked lime ; it is of course a compound of 
lime and water. 

The heat evolved during the slaking, is often suffi- 
cient to set fire to wood, as there are well authenti- 
cated instances of ships having been burned, the 
lime with which they were laden having, owing to 
the vessel springing a leak, absorbed water, and gen- 
raeted heat sufficient to kindle the wood. When the 
quantity of lime is great, and the process is carried 
on in the dark, light is also emitted. 

The origin of the heat is here accounted for, by 
the water entering into union with the earth, and 
becoming solid, following the usual law formerly 
explained, {Seepage 73), that when a fluid becomes 
solid, heat is disengaged, and the cause of the earth 
being reduced to powder is the expansive force of 
the vapour generated by the heat, being sufficient to 
separate the particles; in fact, it is similar to that 
change which some of the neutral salts experience 
18 



206 ELEM£NTS OP CHEMISTRF. 

when Tieated, and which is termed crepitation, (See 
page 182.) 

It has beefi ascertained, that lime, during slaking, 
combines with very nearly one-third of its weight 
of water, 100 pounds taking up about 31. By the 
application of a strong heat to the slaked lime, the 
whole of the water may be driven off, and the earth 
is left pure, and will again undergo the same process. 

Though lime has a very po\v€rful attraction for 
tvater, it is but sparingly soluble. It requires about 
770 parts to dissolve it, and, what is very remarka- 
ble, it is more soluble in cold than in warm water, 
requiring about 1270 of it at a boiling heat. The 
solution called lime water, is transparent and col- 
ourless, and possesses properties similar to those of 
an alkali. It changes the vegetable blues to green, 
as is shewn by adding a few drops of it to cabbage 
water. When exposed to air in an open bottle, or 
saucer, it very soon acquires a crust on its surface, 
which, when broken, falls to the bottom, and another 
is formed. In the course of a short time, the solu- 
tion loses its peculiar taste, and the power of affect- 
ing vegetable blues, the whole of the lime being 
deposited in union with carbonic acid, which it has 
absorbed from the atmosphere, forming what is called 
carbonate of lime. 

When lime itself is exposed to the air, it attracts 
moisture, and is slowly slaked, as when water is 
poured on it ; it at the same time absorbs carbonic 
acid, by which its properties are completely chang- 
ed ; hence the necessity of keeping it, and its solu- 
tion also, excluded from air. 

Lime unites with the acids, and forms some very 
important compounds, by far the most important and 
useful of which, is that with carbonic acid, the carbo- 
nate, forming the different kinds of limestone, 
marble, and chalk, all of which are carbonate of 
lime, mixed with impurities, chiefly siliceous matter, 
and iron. Carbonate of lime is tasteless, it does not 



CARBONATE OF LIME. 



207 



suffer any change on exposure to air, and it is inso- 
luble in water. When subjected to a red heat, it is 
decomposed, the carbonic acid is given off in the form 
of gas, and the lime is left pure. That it is decom- 
posed by heat is proved by a very simple experiment. 
Put some pieces of limestone, marble, or chalk, into 
one end of an iron tube, c^ having its opposite end 
in a water trough, and bring that part containing the 




earth to a red heat, a gas will come off, and may be 
collected ; and which does not support combustion, 
a candle put into it being extinguished. There is 
left in the tube a substance, which, when water is 
thrown on it, is slaked in the same way as lime. 
This experiment, then, proves, not only that the 
limestone is decomposed, but that it is a compound 
of lime and carbonic acid. The decomposition of 
limestone in this way constitutes the method of pro- 
curing lime. For this purpose the limestone, broken 
to small pieces, is mixed with coal, and thrown into 
a kiln, in which a fire has been previously kindled, 
and the heat generated by the combustion is suffi- 
cient to drive off the whole of the acid. As the coal 
is consumed, the lime falls to the bottom, and is raked 
out, through an opening below, while fresh portions 
of the mixture of coal and limestone are thrown in 
from above. In some places a sort of kiln is erect- 
ed of bricks, at the bottom of which is placed some 
straw or coal, and over this alternate layers of coal 
and limestone, and the whole covered with turf, 
leaving apertures below for the admission of air, and 
a vent above for the escape of smoke. The fire 
beneath is then kindled, and the combustion allowed 



^08 ELEMENTS OP CHEMISTRY. 

to continue till the whole of the coal is consumed, 
by which also the carbonic acid is driven oflF. The 
lime is then taken out, and separated from the ashes. 

All the acids decompose carbonate of lime ; they 
unite with the lime, and set free the carbonic acid, 
and hence a method of preparing this gas. Thus, if 
pieces of chalk be put into a retort, and a little muri- 
atic acid, previously mixed with about six parts of 
water, be poured on them, there is an instant effer- 
vescence, and a gaseous fluid may be collected in the 
jar. That this is carbonic acid, is proved by putting 
into it a lighted taper, which is instantly extinguish- 
ed. This experiment also proves, that limestone 
contains carbonic acid, as one of its ingredients ; and 
it is in this way, also, that we know whether lime- 
stone has been properly burned, that is, whether the 
heat has been sujfficient to expel the whole of the 
carbonic acid. If recently burned lime be put into 
water, and a little muriatic acid poured on it, it will 
not effervesce if properly burned, because it does 
not contain any carbonic acid. It is not to be expect- 
ed, however, that the lime offered for sale should be 
entirely free from this acid ; it is seldom so well 
prepared ; besides, by exposure to air, it will absorb 
carbonic acid, w^hich will cause a slight effervescence 
on the addition of the other ; if, however, the effer- 
vescence is great, we must infer that the burning has 
not been properly conducted. 

When water, holding carbonic acid gas in solu- 
tion, is added to lime water, a white precipitate is 
formed. Or if a stream of the gas be passed through 
the solution, the same occurs, the lime being thrown 
down in union with the carbonic acid ; but if more 
of the water or gas be added, the fluid becomes trans- 
parent, the precipitate being re-dissolved by the 
excess of acid. The precipitation and re-dissolving 
of the precipitate, may be shewn, merely by breath- 
ing through the lime water by means of a tube, the 
carbonic acid gas given off from the lungs acting on 



SULPHATE OF LIME. 209 

the lime. The solution thus formed is transparent 
and colourless, but on exposure to air becomes opake, 
from the deposition of the carbonate, owing to the 
excess of carbonic acid escaping ; and hence the 
process by wWioh. peirif actions d^YQ formed. Carbo- 
nate of lime is a very abundant production of nature, 
occurring in dijfferent states, as limesione, chalk, and 
marble, of which there is a great variety. The 
shells of marine animals, and the different kinds of 
marls, are also almost entirely composed of it. Carbo- 
nate of lime exists also in some mineral waters, held 
in solution by an excess of carbonic acid. As the 
water is exposed to the atmosphere, the excess ot 
acid flies off, and the carbonate of lime is deposited ; 
and as the deposition goes on very gradually, it 
adheres to any object in the water; hence the forma- 
tion of petrifactions. Thus, if a piece of moss, or 
the twig of a tree, be put into the water, it appears 
to be gradually changed to a stony matter, w^hich is 
owing to the carbonate of lime deposited, being 
incorporated with it. When the water drops from 
the roof of a cave, the carbonate is also left adher- 
ing to it, and in the course of time it forms large 
projections called Stalactites^ their formation being 
somewhat similar to that of Icicles, 

The uses of chalk and marble are well known. 
Limestone is employed in large quantity for yield- 
ing lime, when exposed to heat. 

Sulphuric acid also unites with lime, and forms a 
sulphate of lime. This is the substance well known 
by the names of Gypsum and Paris Pla^^ter, from 
its being found in great quantities near Paris. It is 
in general of a pale reddish hue, the colour being 
communicated by some metallic matter; but it is 
occasionally found quite white, in which state it is 
called alabaster. Alabaster admits of a fine polish, 
and is often cut into ornaments, as vases and urns. 
Common sulphate of lime, when exposed to heat, 
gives off water, which it contains, and is left purej 
18* 



210 ELEMENTS OF CHEMISTRY. 

and when thus prepared, it has a very powerful 
attraction for water, with which it combines, and 
forms a hard mass ; from which property it is 
employed for taking impressions from moulds, and 
for making statues. For this purpose, it is made 
into a paste, and poured into a mould, previously 
besmeared with a little soap or tallow, to prevent 
them from adhering. It is left there till it become 
hard, and is easily removed. 

Paris plaster when mixed with lime, is also em- 
ployed in forming ornamerits for the ceilings of 
rooms, in which state it is called stucco. In some 
places, particularly where it is abundant, it is used 
as a top dressing for grass lands, arid it is also employ- 
ed as mortar instead of lime. 

Lime exists in great abundance in bones, in com- 
bination with an acid called phosphoric^ because 
phosphorus is one of its ingredients. When bone 
is subjected to a strong heat, the animal matter in it 
is destroyed, and there remains a white porous sub- 
stance, still retaining the form of the bone, and 
which is a compound of lime and phosphoric acid, 
commonly called earth of bone^ or bone ashes. 
This substance, either alone or mixed with clay, is 
used chiefly for making crucibles and pots, more 
particularly when they are to be exposed to a sudden 
heat, as they are not liable to crack by a change of tem- 
perature. It is used also when in very fine powder, for 
taking out greasy spots. For this purpose, it is 
placed on blotting paper, which is put on the cloth 
or paper, and a common smoothing iron, a little 
heated, is drawn over it, by which the grease is 
melted, and absorbed by the powder. Bone earth is 
likewise decomposed with the view of procuring 
phosphorus, which, it has been already mentioned, is 
one of the ingredients of the acid with which the lime 
is in union. For this purpose, the bone, after being 
burned to whiteness, and reduced to fine powder, is 
mixed with ten times its weight of water, and half 



FLUATE OF LIME. 211 

its weight of sulphuric acid, and the mixture kept 
warm for some days. It is then mixed with more 
water, and filtered, by which a fluid is obtained, 
which is the acid of the bones, but still retaining 
some of the lime. It is evaporated to dryness, mix- 
ed with half its weight of charcoal, and subjected to 
a strong heat in an earthen ware retort, previously 
covered with a mixture of sand and clay, and the 
mouth of which is placed in cold water. By the 
heat, the charcoal combines with the oxygen of the 
acid, and comes off in the form of carbonic acid, and 
the phosphorus, the other ingredient, is set free, and 
is given off in vapour, which is condensed in the 
water. As thus procured, it is not pure, but is 
easily purified by putting it into a chamois leather 
bag, melting it under warm water, and squeez- 
ing it through the leather, keeping it all the time 
under the fluid, to prevent it from taking fire. It is 
then poured into small cylinders, the process being 
conducted under water. 

Lime is found also in union with another substance, 
in the mineral called Fluor^ or Derbyshire spar, so 
called, because it exists in great abundance in the 
mines of that county. It is found in crystals of 
different colours, as yellow, green, blue, brown, and 
purple, the last being by far the most common. It 
is also sometimes, though rarely, got colourless. 
When heated gently, it gives out light, the colour of 
which depends on that of the mineral. When treat- 
ed with sulphuric acid, an acid of a peculiar nature 
is disengaged, and which has been long known as a 
powerful corroder of glass, and hence its use for 
etching on this substance. For this purpose the glass 
is covered with a thin coating of wax, and that part 
to be corroded is exposed, by removing the coating 
by a sharp instrument. The spar, reduced to pow- 
der, is put into a metallic vessel, and an equal quan- 
tity of sulphuric acid poured on it, by which the 
acid of the spar is set free ; the glass is then put on, 



212 ELEMENTS OP CHEMISTRY. 

as a sort of cover to the vessel, and secured to it by 
luting, leaving a very small aperture for the escape 
of the superfluous acid. After being on for some 
time, that part uncovered is found to be corroded ; 
if not sufficiently so, the process must be repeated. 
Derbyshire spar is used also as an ornamental stone, 
being cut into vases and urns. 

The action of lime with some of the compound 
salts is important. It has been already mentioned, 
that it has a very powerful attraction for carbonic 
acid, depriving ahnost every substance of it; hence 
its use in decomposing the carbonates of the alkalies, 
with the view of obtaining the alkali in its caustic 
state. When describing the properties of carbonates 
of potassa and soda, {see p, 192.) it w^as stated, that 
it is from them that the pure alkali is obtained, for 
which purpose they are mixed with lime. In decom- 
posi^:ig these salts, different proportions of the ingre- 
dients are used, according to the use to which the 
alkali is to be applied; for as it is never employed 
in its dry state in the arts, it is always retained in 
solution in water, the solution being prepared just 
before it is required. For freeing the salt of its 
carbonic acid, it is dissolved in the requisite quantity 
of water, and then mixed with about an equal pro- 
portion of slaked lime, which unites with the acid, 
and formswith it an insoluble carbonate of lime, while 
the alkali, set free, is held in solution. On allowing 
the fluid to remain at rest, the insoluble matter falls 
to the bottom, and the clear fluid may be drawn off. 
It has been already mentioned {see page 191.) that 
potassa and soda have a very strong attraction for 
carbonic acid, absorbing it quickly from the atmos- 
phere. In this process, then, it is necessary to keep 
the fluid excluded from the air, to prevent the 
absorption of carbonic acid, by which it vt^ould again 
become the same as what was at first decomposed. 
In a similar way soda can be obtained from kelp and 
i)arilia, by mixing them with lime, which deprives 



USES OF LIME. 213 

the carbonate of soda of its carbonic acid ; hence 
the mode practised by soap-makers, for rendering the 
alkali in these substances caustic. For preparing 
solution of potassa, or soda, on a small scale, a similar 
process may be followed. The carbonate of potassa, 
or soda, must be dissolved in about twice its weight 
of warm water. The fragments of lime, in another 
vessel, are mixed with warm water, the quantity 
depending on the required strength of the alkaline 
solution, say with twice its weight, by which it is 
instantly slaked. When the slaking is finished, it is 
to be mixed with the oiher, and after corking the 
vessel, allowed to remain in it till cold. The mix- 
ture is then to be filtered, excluded from air. For 
this purpose it is thrown into a funnel, a, 
^ the throat of which is stuffed with a linen 
rag, and covered with a plate, b ; this 
is to be placed into a bottle, c, through a 
cork or piece of paper, to keep it as tight 
as possible, so as to prevent the admission 
of air. After the filtration has stopped, 
and the mixture in the funnel become 
hard, water is to be poured on it very 
cautiously, which, by its weight, forces out the solu- 
tion still remaining in it ; and this must be repeated 
till the whole of the alkali is drawn through, which 
is found by the fluid that filters through becoming 
tasteless, or not changing; a vegetable test paper. It 
is known when the solution of potassa, or soda, is 
freed entirely of its carbonic acid, by mixing with it 
some lime water. If it should still retain a little of 
it, it will become turbid, from the deposition of 
carbonate of lime. 

Lime, in its pure state, is much used for various 
purposes- From its powerful attraction for water, it 
is employed for keeping dry, substances that are 
liable to be injured by moisture. For this purpose, 
a quantity of recently burned lime is placed at the 
bottom of a box or tin cannister, and over it are put 




214 ELEMENT^ OF CHEMISTRY. 

the substances to be kept dry, by which the air in 
the cannister is always deprived of its moisture by 
the lime. When the lime seems to be slaked, which 
is known by the whole of it being reduced to powder, 
it must be renewed. In this, iron instruments may 
be kept from being rusted, and other substances from 
being injured by moisture. Lime is also employed 
in glass-making, and in the manufacture of soap, in 
the last of which it deprives the alkaline carbonates 
of their carbonic acid. 

The principal uses of lime, however, are in agri- 
culture and in building. For the former, it is 
employed either as procured from the quarry, that 
is, in the state of lim.estone or carbonate, or after 
being burned. When recently burned lime is mixed 
with vegetable matter, it acts on it, and forms a sort 
of compost, part of which is soluble in Vv'ater, and 
thus it renders nutritious, some of that which was 
formerly inert. It is in this way that it is supposed 
to act in fertilizing soil that abounds in vegetable 
matter, as the roots and stems of the crop previously 
cut ; of course, its action must be the same, when 
used for cultivating waste ground. Mild lime, as it 
is called by farmers, or limestone, has no action of 
this kind; on the contrary, it prevents the too rapid 
decomposition of vegetable matter, so that, when 
soil abounds with this, already in the same state as 
that produced by the action of quick-lime, mild 
lime is used ; and for this purpose, that called marl 
is employed, which is merely the fragmente of shells, 
or substances containing carbonate of lime. 

Lime is employed as mortar, in two different 
ways, either for dry building, or for building under 
water. In preparing mortar for the former purpose, 
the lime is first slaked, and after being sifted, to free 
it from impurities, it is mixed with sand, and made 
into a paste with water, which must be well 
beat, that the materials may be intimately incorpo- 
rated. 



MORTAR. 215 

It is a subject of common regret, that mortar, as 
now made, is far inferior to that used by the ancients, 
from which it is supposed, that they must have had 
some mode of preparing it with which we are unac- 
quainted. The imperfection in this article is, how- 
ever, to be ascribed more to carelessness, than to 
ignorance of a good method of making it; for when 
great attention is paid to the process, it can be pro- 
cured equal to that in old buildings. 

The first thing to be attended to, is the choice of 
the lime, which, if possible, ought to be of a brown- 
ish colour, as it forms a harder cement than that 
nearly colourless. It must of course be well burned, 
so as to be easily slaked, after which it must be pass- 
ed through sieves, that the stony impurities and 
unslaked part may be removed. It is also of mate- 
rial consequence to be particular with respect to the 
sand ; the sharper and coarser it is, so much the 
better, as it requires less lime, and forms a harden 
cement than the finer kind. Pit sand is preferable 
to that from the sea shore, as the latter contains 
impurities, which prevent the hardening of the mor- 
tar. The same is, however, the case with the former, 
if it contain clay, which it sometimes does ; so that, 
when pit sand is used, it must be chosen as pure as 
possible. Particular attention must likewise be paid 
to the mixing of the materials, for the more inti- 
mately they are blended, the more completely does 
the mortar become hard. The mixture ought there- 
fore to be well beat with a wooden mallet, till it does 
not adhere to it. It is also the better for being kept 
for some time, provided it is excluded from the air, 
to prevent it from absorbing carbonic acid, for which 
reason it must be covered with sand, and before it is 
used, it must again be beat up with the mallet. 
Another kind of mortar is employed for building 
under water, as that already mentioned does not 
harden in it. . The substance used by the Romans 
for this purpose, is that called puzzolana^ a light 



216 ELEMENTS OF CHEMISTRY. 

porous body, of a reddish colour, said to be lava from 
Vesuvius. In preparing mortar with this, it is redu- 
ced to coarse powder, and mixed with lime, either 
with or without sand, in which state it very soon 
hardens even under water. Of course the same pre- 
cautions must be followed as in the preparation of 
common mortar, with respect to the mixing of the 
materials. The best proportions seem to be about 
equal parts, by measure, of slaked lime and puzzolana. 
In some cases, where the building is not much expos- 
ed, the quantity of the latter may be diminished, and 
sand substituted. The substance called tarras^ made 
use of by the Dutch, is merely a sort of whin-stone, 
reduced to powder, and employed in the same way 
as puzzolana, but the proportions of the materials 
are different; it is commonly mixed with twice its 
bulk of lime, to which occasionally three of coarse 
sand are added. Other substances are used in some 
countries for a similar purpose, as common whin- 
stone, and iron-stone, which, when properly mixed 
with lime, afford a mortar that hardens under water. 
Connected with the use of lime in making mortar, 
is its employment in the preparation of cements. A 
cement is a substance, used for joining bodies, or 
for covering them, to keep them from being ftcted on 
by fire or some other agent; of coarse its nature 
differs according to the use to which it is applied, 
but in manj^, lime forms a principal ingredient. The 
most common cement containing it, is that made 
with white of eggs. It is prepared by beating well 
together, equal quantities of white of eggs and water, 
and then mixing with it as much slaked lime as will 
bring it to the consistence of thin paste, in which state 
it is applied to the places to be joined. Or it 
may be spread on paper or linen, w^ith which the 
juncture must be covered. Another way of using 
this cement, is to spread the white of eggs, on paper, 
and sprinkle it with the powder of lime. Instead of 
white of eggs, a solution of isinglass or glue in warm 



CEMENTS. 217 

water is employed. Though the cements mention- 
ed are not apt to be affected by water, they do not 
answer for preventing the escape of noxious vapours, 
others must therefore be used. The most common 
of these, is drying oil, made into a thick paste with 
lime, or with white lead, which answers equally well ; 
indeed, what is now commonly used, is merely white 
lead paint, which, when applied to junctures, becomes, 
after standing some time, quite hard, and is not acted 
on by water; hence its frequent use in cementing glass. 
A cement of a similar nature is made with cheese and 
lime. It is prepared by boiling in water, the poor- 
est skimmed milk cheese, till it becomes soft, after 
which the fluid is poured off, and it is then well 
kneaded, first in cold, and then in warm water, and 
mixed with quick-lime, in which state it is applied 
to the junctures. It answers well for joining pieces 
of earthen ware, glass, or marble. 

Cements of a different nature are used for fixing 
bodies to each other, particularly on a large scale. 
Thus, 7 parts of common resin, and 1 of wax, melt- 
ed, and mixed wMth powder of lime, or with Paris 
plaster, brick dust, or red ochre, form a good cement 
for many purposes, when the articles are not to be 
exposed to heat, as for joining glass apparatus to each 
other, or to metal or wood, as in adapting brass caps, 
or in erecting electrical machines. The substance 
used for fixing handles to knives and forks, is of 
this nature. It is prepared by mixing pitch, resin, 
and brick dust, and applying it when liquid. A 
softer kind of cement is made by melting together 
8 of wax, and 4 of resin, and mixing with them 1 of 
oil. This, vs^hen cold, congeals, but it is easily soft- 
ened, by working it between the fingers, in which 
state it is applied, or it may be put on, by holding it 
on a warm wire, and allov/ing it to flow on the junc- 
ture. It is much used for luting glass apparatus, 
and for securing stoppers in bottles, to prevent sub- 
stances in them from absorbing air or moisture, or 
19 



218 ELEMENTS OP CHEMISTRY. 

for retaing some of the gases, which cannot be kept 
over water. 

For cementing precious stones, gum mastick is 
commonly employed. For this purpose, it is dissolv- 
ed in spirit of wine, to which is added a solution of 
isinglass, in rum or brandy, with which a little gum 
galbanum, or gum ammoniac, has been mixed. The 
whole is rubbed together, a gentle heat being at the 
same time applied. It must be kept in well stopper- 
ed bottles, and if it become hard, it can be softened 
by the application of a slight heat, as by plunging 
the bottle into warm water. A cement of a similar 
nature is prepared by mixing a solution of shell lac 
with one of isinglass, and which may be made much 
stronger, by adding some finely powdered pumice 
stone, or it may be prepared, by melting in a ladle 
equal weights of shell lac and pumice stone, reduced 
to very fine powder, stirring; them well, till they 
become quite incorporated. When required for use^ 
it is softened by the application of heat. This is 
employed by some lapidaries, for fixing precious 
stones when grinding or cutting them. Coarser 
kinds of cements are used for joining covers to ves- 
sels, as to pots or crucibles, which are to be exposed 
to a strong heat. The most common of these, is a 
mixture of pipe clay and sand, or brick dust, made 
into a thick paste with a strong solution of borax. 
This is also often employed, for coating the outside of 
vessels, as crucibles, earthen ware retorts, or tubes, to 
prevent them from cracking when heated, or to pre- 
serve them from the action of fire. In applying it, 
it may be made into a thick paste, with which the 
vessel must be coated, or it may be made thin, and 
the vessel dipt into it, by which a little will adhere. 
This is to be allowed to dry, and the process repeat- 
ed, till the covering becomes of sufficient thickness. 
For filling cracks in iron vessels, or for joining iron 
tubes together, a mixture of iron filings, sulphur, 
and sal ammoniac, is employed. For this purpose* 



BLEACHING. 219 

2 ounces of flowers of sulphur, 1 of sal ammoniac 
in powder, and 16 of iron filings, are mixed, and 
passed through a fine seive. To this 20 pounds of 
iron filings are afterwards added, and when to be 
used, the mixture is made into a paste with water^. 
and applied to the juncture. 

Lime is now very much employed for preparing 
the substance used in bleaching. It has been already 
remarked, when describing the properties of chlorine, 
that from the power which it has of destroying colour, 
it is used with the utmost success in bleaching. When 
first introduced, it was emploN^ed in the gaseous form, 
and aftervvards in solution ; but these, though very 
efficacious, proved extremel}^ injurious to the work- 
men ; the process has therefore undergone several 
alterations, the principal of which consists in uniting 
it w^ith lime, by which it is in a great measure de- 
prived of its noxious qualities, and can be transported 
with greater ease from the manufactory to the bleach- 
field. 

Before proceeding to describe the process as now 
conducted, it may not be uninteresting to detail the 
steps according to the old method, not only as in 
many parts the}' agree, but as it affords a good exam- 
ple of the great improvement which some of the 
arts have received from chemistry. 

The first part of the process, according to tlie old 
mode, was the steeping^, wiiich consisted in keep- 
ing the cloth for some days in cold water, or in a 
very weak solution of potassa, so that the impurities 
might be loosened and dissolved, the potassa acting 
on the greasy matter in the cloth, and forming with 
it a kind of soap, after which it w^as well washed. 
The next operation was bucking, or boiling the 
goods in an alkaline solution, or what the bleachers 
call a lei/, after which it was exposed on the ground 
for two or three weeks, and again bucked, washed, 
and exposed on the ground. These were in general 
repeated four or five difierent times, the ley being 



■^20 lELEMENTS OF CHEMISTRY. 

made gradually weaker. After the cloth had been 
subjected to these different processes, it was next 
exposed to that of souring, which consisted in soak- 
ing it in milk that had been allowed to become sour, 
in which it remained for two or three weeks, after 
which it was removed, and again submitted to the 
processes described, till it appeared to be quite clean- 
ed. In the last washing, soap was generally used, 
by which this was more easily accomj.lished. It has 
been already mentioned, that the alkali, in the process 
of bucking, loosened the foreign matter. The sour- 
ing, containing a small quantity of acid, destroyed 
the properties of the alkali, by combining with it, 
and thus prevented it from acting on the cloth, when 
exposed on the ground ; at the same time, by wash- 
ing between each operation, any excess of alkali or 
acid was removed, and it was thus left in a state fit 
for being whitened by exposure to air. In this last 
part of the process, it was supposed to be the oxygen 
of the atmosphere that acted on the colouring matter, 
and imparted whiteness to the cloth. 

The iDleaching process now described, was extreme- 
ly tedious. When begun in March, it was seldom 
finished till September, and when the web was not 
sent till about May, it was only half bleached that year, 
and finished in the spring of the succeeding. About 
the middle of the last century, a great improvement 
was introduced, by substituting for sour milk, very 
much diluted oil of vitriol, by which the process was 
shortened ; indeed, it was completed in about half the 
time, for each souring did not require more than 
from 12 to 24 hours, whereas that with milk continu- 
ed for several weeks. The most important improve- 
ment, however, was the introduction of oxymu- 
riatic acid, or chlorine. vSoon after this substance 
was discovered, Berthollet, a French chemist, shew- 
ed that it might be used with the utmost success in 
bleaching, after which it was very soon applied to 
this purpose in Great Britian. It was first used in 



BLEACHING. 221 

the gaseous form, the cloth being suspended in apart- 
ments filled with it, but for which its solution in 
water was soon substituted. 

Though bleaching had thus received a very great 
improvement, with respect to the shortening of time, 
and diminution of labour, it was found that the newly 
discovered substance proved extremely injurious to 
the workmen ; other methods of using it were ac- 
cordingly tried, the first of which was that of com- 
bining it with solution of potassa, or lime, which 
were equally efficacious, without being in the least 
noxious, or even disagreeable ; but it still possessed a 
disadvantage, the inconvenience of conveying it from 
the manufactory to the bleaching ground. This was, 
however, soon obviated by Mr Tennant of Glasgow, 
who discovered a mode of combining it with lime 
in its dry state, in which form it is easily transport- 
ed in barrels. The bleaching compound now used, 
and which is called by bleachers oxymuriate of lime j 
is prepared merely by passing the gas through slaked 
lime kept in vessels, in which it is constantly agitated 
by machinery. After it ceases to be absorbed, the pro- 
duct is removed, put into barrels, and kept as much 
as possible excluded from air. 

In the process of bleaching as now conducted, the 
cloth is submitted to the previous steps of bucking 
and souring, four or five difierent times, being well 
washed after each operation. It is then put into a 
solution of the bleaching compound, in which it 
remains for some time, after which it is washed, and 
again submitted to the process of souring and steep- 
ing. This immersion into the bleaching fluid is 
repeated several times, according to the nature of 
the cloth, being soured, steeped, and washed, after 
each immersion. When these are finished, the cloth 
acquires a yellow tinge, but which is easily banished, 
by exposing it on the ground for a few days, after 
which it is boiled for a short time in a weak solution 
of potassa and soap, and again washed. 
19* 



222 ELEMENTS OF CHEMISTRY. 

Since the introduction of the bleaching compound^ 
the whole process never requires more than five 
weeks, even with large webs, and a small piece of 
cloth may be finished in a few days. Besides this 
very great improvement, the new process has other 
advantages ; the cloth is not so apt to be destroyed, 
for, in the old mode, the repeated operations to which 
it was subjected tended to weaken it, whereas in 
this, the impurities only are removed. 

The process of bleaching now described, is that 
practised with linen goods; with cotton there is no 
necessity for the latter part of it, as it does not acquire 
the yellow tinge by the use of the bleaching com- 
pound. 

The bleaching of hose difiers a little from that of 
cloth. As mutton suet, dissolved in soap, is used 
by weavers, it is necessary to remove it, before 
attempting to bleach them. This is done by first 
scouring them with warm water and soap, and after- 
wards boiling them in a weak solution of potassa. 
They are then alternately immersed into a solution 
of the bleaching substance, and boiled in an alkaline 
ley different times, by which they are completely 
bleached. They still, however, contain impurities, 
derived from the substances used in the process, but 
which are removed by soaking in diluted acid, and 
alkaline solutions, and washing with soap and water, 
to the last of which a little indigo is added. It is 
found by bleachers, that if any of the soap is left in 
the hose, they acquire a yellow colour on keeping, 
but which is prevented, by exposing them to the 
fumes of burning sulphur, which is said to decom- 
pose the soap, and prevent it from tinging the goods ; 
hence the disagreeable odour woollen stuffs in general 
have, which, however, leaves them after they have 
been washed. 

The principal circumstance to be attended to in 
bleaching according to the new process, is to take 
care that the goods are well washed after each ope- 



BLEACHINiJ. 223 

ration, and that the solution of the bleaching sub- 
stance is not too strong, as it is then apt to injure 
the cloth. To ascertain this, bleachers have in gene- 
ral what is called a test Jluid, which is merely a solu- 
tion of indigo in weak oil of vitriol. In preparing 
the bleaching fluid, it is made of such strength, that 
a certain quantity of it must destroy the colour of a 
certain quantity of the indigo solution. It is with 
the same view also, that weavers often run a coloured 
thread along the end of their goods, by which they 
know if the bleaching fluid has been of proper 
strength, for, when properly prepared, it ought 
to bleach without destroying the colour of the 
thread. 

Before finishing this subject, it may here be re- 
marked, that a solution of the bleaching substance 
is very efficacious for removing the yellow tinge, 
which linens always acquire by being w^orn. For 
this purpose, they are kept for a few days in a weak 
solution of it, and then well washed, the solution 
being prepared by dissolving a tea-spoonful in a 
quart of water. It is also much employed for 
taking out ink spots from cloth, or paper. This is 
done by applying the solution, by means of a hair 
pencil, to the part soiled, and after it has remained 
on for some time, washing it off with cold water. 
Should the spot not be removed by the first process, 
it must be repeated, taking care to wash w^ell after 
each application. It may even be applied to printed 
paper, or copper-plate impressions, as it does not act 
on the inks used by printers and engravers. 

When the bleaching compound cannot be procured, 
a solution having the same power is easily prepared. 
For this purpose, two ounces of the substance called 
black oxid of manganese, but usually sold under the 



224 



ELEMENTS OF CHEMISTRY. 



name of manganese, is put into a retort, A, and on it 
is poured four ounces of muriatic acid; a receiver, B, 




is adapted to the retort, in which there is an ounce 
of potassa dissolved in three or four of water. 
Heat is applied, by which chlorine gas is driven off, 
and, passing through the solution in the receiver, is 
absorbed. If a little of this be put on an ink spot, 
it destroys it, and it may be used for removing the 
dingy colour of linens, having previously diluted it 
v/ith a good deal of water. 

ALUMINA. 

Alumina, so called from its being the base of 
alum, has had various other names, as t^rgill, from 
its existing in clay, and Fuller^ s Earth, from a par- 
ticular use to which it is applied. When pure, it is 
a white powder, tasteless, insoluble, and having a 
greasy feel. It is not, however, put to any particu- 
lar use in this state ; but it combines with the acids, 
and forms some very important salts, used by dyers 
and calico-printers. The most common and the most 
interesting of these is alum^ which contains the 
earth in Union with sulphuric acid and an alkali, 
either potassa or soda. Alum is obtained in large 
crystals, of a pyramidal shape. It has a sweetish, 
astringent, taste ; when exposed to a dry atmosphere, 
it effloresces, but in one of moderate moisture, it 



ALUMINA. 225 

does not undergo any change. It is soluble in about 
20 parts of cold, and in about its own weight of 
boiling water. The solution is transparent and col- 
ourless, and possesses the property of reddening vege- 
table blues; hence it must contain an excess of acid. 
When subjected to a moderate heat, it becomes fluid, 
undergoing watery fusion; and by continuing the 
heat, the whole of the water is expelled, and a dry, 
spongy mass is left^ commonly called burnt alum. 
This is easily done by placing it in a saucer over a 
fire. 

When the solution of an alkali, as that of potassa, 
is added to solution of alum, a white powder is 
thrown down, which is the earth alumina, in a state 
of purity ; but if more potassa be put in, the powder 
disappears, being dissolved by the excess of alkali. 

Alum is in some places a native production, exist- 
ing in some rocks ; in others it is prepared arti- 
ficially. Alum ores, as they are called, contain, in 
general, sulphur, iron, alumina, and a small quantity 
of potassa, and from these alum is procured, the pro- 
cess differing in diiTerent places. The simplest con- 
sists merely in exposing the ore, moistened, to the 
atmosphere, and stirring it occasionally, so as to pre- 
sent a new surface, by which the whole of the sul- 
phur unites with the oxygen from the air, and be- 
comes sulphuric acid, which then combines with the 
alumina and potassa to form alum. The remaining 
part of the process consists in washing the product, 
filtering, and evaporating, by which crystals are 
obtained. In some places the ore is roasted, by burn- 
ing it with coals or brushwood, and keeping it ex- 
posed to heat for a considerable time, by which, also, 
the sulphur attracts oxygen, and becomes sulphuric 
acid, to unite with the alkali and earth. When the 
ore does not contain potassa, some of this must be 
added, otherw^ise alum is not formed. For this pur- 
pose, the residue of the operation of soap-makers, 
which contains potassa in union with muriatic acid, 



226 ELEMENTS OF CHEMISTRY. 

is employed, and the alkali of which unites with the 
sulphuric acid and alumina, to form alum. 

Alum is used in large quantity in the arts. When 
added to tallow, it imparts hardness to it ; hence it 
is used by candle-makers. When a little of it is mix- 
ed with milk, it makes the butter separate more 
quickly ; and wood or paper impregnated with it, 
as by soaking/them in its solution, does not easily 
take fire. Alum is, however, used chiefly by dyers, 
in whose operations it serves a double purpose ; it 
opens the pores of the cloth, and renders it fitter to 
receive the dye stuff, and it unites also with the col- 
ouring matter, and thus renders it more fixed. That 
alum has a strong attraction for colouring matter is 
. shewn, by mixing its solution with that of any colour, 
as madder or cochineal, and then adding potassa ; 
the alumina is thrown down, taking with it the whole 
of the colour, with which it is intimately incorpo- 
rated, and hence a method of preparing some paints. 

Alumina is a very abundant production. The alu- 
minous fossils have not any characters that can be as- 
signed to the whole of them, they difffir so much from 
each other. Some of the hardest and richest gems 
are almost entirely composed of it, and the different 
kinds of clay are nearly of the sam.e composition. 
The oriental ruby, sapphire, topaz^ amethyst, and 
emerald, are all of this kind. The oriental sapphire 
has no less than 9Si percent, of alumina. The most 
abundant of the aluminous productions, however, are 
the clays, among which are porcelain clay and pot- 
ters' clay, both employed in the manufacture of dif- 
ferent sorts of earthen ware. These, along with alu- 
mina, contain lime, magnesia, the earth of sea sand, 
and iron ; the fusibility depends on the proportion 
of alumina, and the colour is imparted by the metal. 

SILICA. 

Silica^ or the earth of sea sand, is a very abun- 
dant production. When pure, it is a white powder, 



siiLCA. 227 

tasteless, insoluble, and requiring a very intense heat 
for its fusion. The heat excited by the rays of the 
sun, concentrated by a large lens, or by the combus- 
tion of charcoal, animated by a stream of oxygen, is 
riot sufficient to fuse it. It may, however, be melted 
by the oxy-hydrogen blow-pipe. Silica is one of 
those substances that resists the action of almost all 
chemical agents ; those with which it acts most 
easily are the alkalies potassa and soda, WMth w^hich, 
when heated, it unites, and forms compounds, differ- 
ing in their properties according to their proportions. 
When the alkali is in large quantity, a substance is 
produced, which is soluble in water ; but when the 
silica is in excess, a matter of a very different nature 
is formed, the product of their union being glass. 

Though this beautiful production of art is obtained 
by the union of silica and an alkali, other substances 
are added, to impart to it particular properties, such 
as lime and litharge, the latter a compound of lead 
and oxygen, the uses of which will be afterwards 
mentioned. 

There are different kinds of glass, according to the 
substances employed in its manufacture, such as bot- 
tle glass, flint glass, window, broad, and plate glass. 

Bottle glass is in general made by exposing to heat 
common sea sand, which is almost entirely silica, 
and the refuse of the operation of soap-makers, w^hich, 
along with potassa, contains a large quantity of lime, 
with some alumina, magnesia, and silica. 

Window glass is formed from sand, and kelp or 
barilla, and the finer kinds of glaas are manufactured 
from potassa, or soda, and very pure sand, or, w^hich 
is better, powdered flints, these being almost entirely 
composed of silica. 

In the manufacture of glass, the substances are 
separately reduced to powder, and afterwards well 
mixed. They are then thrown into a kind of furnace, 
or oven, and heat applied to them, by which the 
moisiure is expelled, part of the fixed air is driven 



22S ELEMENTS OP CHEMISTRY. 

off from the alkaline matter, and the inflammable sub- 
stance is consumed ; at the same time, an action takes 
place between the silica and alkaline matter. In this 
part of the process, which is called fritting^ great 
care must be taken not to apply too much heatj oth- 
erwise a considerable part of the alkali is sent off in 
vapour ; the mixture should also be constantly stirred, 
to allow the whole of the carbonaceous matter to be 
consumed, by its coming in contact with the air, and 
to prevent it from running into hard lumps. After 
this, the substance is removed from the furnace, and 
set aside to cool, in which state it is termed /rzY. 

When frit is again to be melted, for the purpose of 
making glass, it is put into large conical vessels of 
baked clay, previously heated, each of which holds 
about 20 cwt. In these it is exposed to a high tem- 
perature for about two days, by which the whole 
becomes fluid, and passes into the state of glass. 

During this part of the process, a quantity of saline 
matter collects at the top, called sandiver or glass- 
gall, which is removed by means of iron ladles. 
After this, the heat is continued, till portions of the 
glass, when taken out and cooled, do not present a 
speckled appearance. It is then 3aid to be refined, 
and its temperature is allov/ed to fall, till it becomes 
so thick that it can be wrought into the various articles. 

In the formation of the articles of glass, the work- 
man dips a hollow cylinder of iron into the melted 
matter, by which a small portion of it sticks to the 
metal. He then, by blowing through the tube, and 
rolling the glass on a smooth iron plate, models it 
into any form he chooses, as wine glasses, decanters, 
and phials. Green bottle glass is wrought in the 
same way, but the bottle is blown within a mould. 

Plate glass is prepared by casting the melted matter 
on ver}^ smooth horizontal metallic tables, on which 
it is allowed to cool. 

The manufacture of window glass is by far the 
most interesting. When the fused substance has 



GLASS. 



229 



been brought to the proper state, the workman dips 
his iron tube into it, and allows what is collected on 
it to cool, and by repeated dippings and cooling, he 
gathers as much as he thinks is sufficient to make 
what is called a table of glass. Having done this, 
it is rolled along a polished iron plate, to give it a 
cylindrical form, the workman at the same time blow- 
ing through the tube, by which it acquires a pear 
shape. By holding it in the furnace, he again softens 
it, and by blowing into it enlarges it, which he does 
repeatedly, till he at last makes it of a pyramidal 
form, with a flat bottom, and rounded sides, a. 
Another workman then dips a solid rod of iron into 

the melted glass, and 
attaches it to the cen- 
tre of the base of the 
pyramid, b ; after 
which the tube c, is 
taken off, by touching 
the glass, at a little 
distance from where it 
is connected to it, dj 
with a cold iron rod, 
by which a crack is 
produced. By asmart 
blow it is detached, 
leaving a hole of about 
2 inches in diameter, 
in the point of the 
cone. This part of it 
is then exposed to 
heat, by holding it at the mouth of a furnace, after 
which the whole of it is heated, till it becomes quite 
soft; the workman gives the iron rod, 6, a circular 
motion, by rolling it between his hands, w^hich he 
gradually makes quicker and quicker, and by this 
means the hole in the pyramid is enlarged, and at 
last it suddenly flies open, and forms a circular plate, 
efy of about four feet in diameter, of uniform thick- 
20 




230 ELEMENTS OP CHEMISTRY. 

ness, except where the rod, b, is fixed to it, which 
is now detached by a process similar to that already 
mentioned. 

Broad glass is made by blowing a hollow globe, of 
about a foot in diameter, which is placed at the 
mouth of the furnace ; the side of it is then touched 
with a cold rod, so as to occasion a crack that runs 
longitudinally, and as the glass is softened by the 
heat, the crack by degrees opens, and at last the ball 
is converted into a thin sheet. 

Though silica and the alkalies, by their union, pro- 
duce glass, other substances are added to make it 
more perfect, such as the oxides of lead and manga- 
nese, and sometimes also a little nitre. Various 
ingredients are likewise employed, to give it partic* 
ular qualities. 

When glass is prepared from kelp or barilla, it 
always acquires a greenish tinge, from the iron which 
they contain. To prevent this, black oxide of man- 
ganese is mixed with the fused matter, to afford 
oxygen to the iron, by which it passes into that 
state, that it either does not combine with the glass, 
or if it does, does not colour it. Oxide of manganese 
itself makes glass purple, but by being deprived by 
the iron of a portion of its oxygen, it also passes into 
that condition that it does not communicate any col- 
our ; great care must therefore be taken to add the 
due quantity, for if too much be employed, the 
glass will have a purple tinge ; whereas, if too 
little be used, the whole of the iron will not be act- 
ed on, and it will retain a little of the green. When 
too much manganese has been used, which is known 
by removing a little of the fused matter, and allow- 
ing it to cool, it can be easily destroyed by thrusting 
pieces of wood into it, so as to deprive it of its 
oxygen, and form carbonic acid, which is expelled 
by the heat. 

Nitre is occasionally also employed for destroying 
the green tinge communicated by iron, acting in the 



ANNEALING. 231 

same way as the manganese, by affording oxygen to 
it, and causing it to pass into that state that it will 
not impart colour. 

Compounds of lead, such as litharge, are always 
mixed with the ingredients of glass, proving very 
powerful fluxes, and thus causing the substances to 
melt more easily. They also impart greater density, 
and increase the lustre of the glass ; and they make 
it more tenacious, consequently more easily wrought 
into the different articles. 

If glass, after it has been fused, be hastily cooled, 
it is easily broken by the slightest agitation. Hence 
we often find that it cracks without any apparent 
cause ; but this is prevented by the process of an- 
nealings to which it is subjected imm^ediately after 
it is manufactured. Annealing consists in placing 
the glass in a long oven, the heat of which is consid- 
erably below that necessary for its fusion, and which 
is hotter at one end than the other. The articles are 
put in at the warmest extremity, and gradually drawn 
from this to the colder one, and, w^hen almost cold, 
they are removed. As the first set comes out at the 
one end, a second is put in at the other, and in this 
way the oven is kept always full. 

During this process, it is supposed that the gradual 
reduction of temperature allows the particles of the 
glass to arrange themselves properly ; whereas, when 
quickly cooled, they are prevented from assuming 
that arrangement, and the slightest cause is sufficient 
to rend them asunder. On the proper annealing, 
then, depends entirely its capability of standing 
sudden applications of heat or cold. That glass 
w^hich is not annealed is easily broken by exciting a 
slight vibration in its particles, can be shewn, by 
forming a tube, and allowing it to cool without an- 
nealing. If a small piece of flint be thrown into it, 
it is instantly broken. The same is the case with the 
green glass substances, called Rupert's drops, which 
are formed by allowing the melted glass to fail into 



232 ELEMENTS OF CHEMISTRY. 

water. If the end of the tail be broken off, the 
vibration excited among the particles instantly shat- 
ters it to pieces. 

It is a remarkable fact in the making of glass, that 
if the fused matter be allowed to cool very slowly^ 
as is the case when the furnace cracks, and its con- 
tents escape, it loses entirely its transparency and 
lustre, and resembles a stony body, becoming much 
less fusible than before ; but if at\er this it be again 
melted, and cooled quickly, it resumes its former 
appearance. This has been proved to depend entire- 
ly on the quickness with which the matter after 
fusion passes into the solid state, a piece of green 
bottle glass having been made to undergo these 
changes repeatedly, by fusing it, and at one time 
making it cool slowly, and at another quickly. It 
is not known how this acts ; the gradual cooling 
may allow the particles so to arrange themselves, as 
to make the substance opake, but the difference in 
fusibility cannot be accounted for. 

On this property depends the method of convert- 
ing glass into what is called Reanineur'^ s Porcelain, 
For this purpose, after being modelled into any par- 
ticular article, it is surrounded with a bad conductor 
of caloric, as finely sifted ashes, or Paris plaster, and 
then exposed to heat, less than what is sufficient to 
melt it, and during the slow cooling, it loses entire- 
ly its transparency, becomes less fusible than before, 
and not so liable to break by a sudden application 
of heat or cold. 

Though glass, as generally made, is transparent 
and colourless, a variety of colours can be imparted 
to it, by the addition of metallic compounds. The 
metals unite with oxygen, and form substances 
resembling the earths in many of their properties, 
and when melted with glass, combine with it, and 
communicate colour, without diminishing its trans- 
parency and lustre, provided they be employed in 
proper proportion. Those generally used for this 



EARTHEN WARE. 233 

purpose, are oxide of gold, which gives a red colour, 
resembling that of a ruby, iron, which imparts a 
variety of colours, according to its state of combina- 
tion. It has been already mentioned, that the green 
tinge of bottle glass is owing to iron ; when in larger 
quantities, the glass is yellow or brownish. The 
compounds of copper communicate a green colour, 
similar to that of an emerald, while antimony gives 
a yellow. Oxide of manganese, it has been already 
stated, is added in small quantity to destroy the col- 
our given by iron ; but when too much is employed, 
it imparts a purplish tinge ; hence its use in making 
purple glass, the appearance of which depends en- 
tirely on the quantity employed. When glass is 
fused with compounds of cobalt, it becomes of a rich 
blue colour ; of course, if antimony be employed at 
the same time, it makes it green, which is produced 
by the blue of the one, and the yellow of the other. 
The metal called chrome, imparts to glass difierent 
colours, according to the compound employed, as red 
and green ; and as the colours communicated by it 
are far superior to those of other metals, it is much 
used in imitating gems, as emeralds and rubies. 

Glass is often rendered opake, forming what is 
called enameL This is done by the addition of a 
large quantity of a metallic compound, which does 
not colour it. The most common is oxide of tin, 
w^hich renders it white and opake, and by the addi- 
tion of other metallic compounds to this, different 
colours may be given it. Another white enamel is 
formed, by mixing burnt bones with glass, but it is 
not so fine as that with tin. These enamels are used 
chiefly as a coating to metals, as in making dials 
for clocks and watches. 

Another process depending on the union of silica 
with other bodies, is the manufacture of earthen 
ware, no less interesting in all its stages than that of 
glass. The substances employed are the different 
kinds of clay, in which silica exists in large quan- 
go* 



234 ELEMENTS OP CHEMISTRY. 

tity ; but it is the alumina which they contain, that 
gives them the properties that render them fit for 
this manufacture. Lime also exists in them ; but if 
it be in great quantity, it makes them too fusible, 
A little iron is also present, which gives to them a 
reddish or brown colour. On the purity, then, of 
the clays, depends the fineness of the earthen ware. 
The substances used in China are very pure. There 
are two kinds, the one called Kaolin, the other 
Petuntsee ; 100 parts of the former being composed 
of 74 silica, IQ^ alumina, 2 lime, and 7 water 5 the 
latter, of 74 silica, 14J alumina. 

In Europe the clays are not in general so pure ; 
hence the difficulty of imitating China. In some 
places, however, very fine clay has been found, and 
in these earthen ware of a superior quality is made. 
Magnesia is occasionally added to clay, to prevent, 
as some suppose, the contraction which it suffers on 
exposure to heat : but if too much be employed, it 
adds to the fusibility of the mixture. The coarser 
kinds of clay are used for inferior articles, as cruci- 
bles, &c. 

In the manufacture of the finer earthen ware, the 
clay is mixed with siliceous matter, as pure white 
sand, or the fine powder of flints. To prepare the 
latter, the flints are exposed to heat in a kiln, similar 
to that in which limestone is burned, by which they 
become brittle, and are easily powdered. 

The clay is prepared nearly in the same way, after 
which it is mixed with water, and well kneaded with 
wooden instruments till it becomes a uniform mass, 
in which state it is mixed with the powdered flints, 
also made into a paste. The mixture, when fluid, is 
then passed through fine sieves, and poured into 
brick troughs, in which it is exposed to heat, till, by 
the expulsion of the water, it becomes of proper 
consistence. After this, it is again well kneaded^ 
by beating it with wooden mallets, and working it 
with the Ixands; till all air bubbles disappear. It ts 



PORCELAIN. 235 

then in a condition fit for being moulded into any 
shape, which is done with the finer kinds of ware, 
by casting it in moulds, and with the coarser sort, by 
forming it on a wheel. The wheel employed in the 
formation of stone ware utensils, is a round board 
attached to a lathe, which makes it revolve in a hori- 
zontal direction. On the centre of this the prepared 
clay is put, and the wheel is turned, during which 
the workman, either by his hand, or by means of a 
piece of wood, models it into any shape he pleases. 
In this way, conical, cylindrical, and round vessels^ 
are formed ; all others are made in moulds. 

The articles thus prepared, are dried either in the 
air, or in stoves slightly heated, after which they are 
put into pots of baked clay, and heaped up in a tall 
oven. A moderate heat is then applied, but which 
is afterwards gradually increased, and continued for 
two days and nights ; they are then removed, and in 
this state the ware is called biscuit. It is to this 
that the figures are generally imparted. For this 
purpose, an impression from a copperplate is thrown 
off on thin paper, which is put when moist on the 
biscuit, and gently struck with a flannel roller, and 
after remaining on for a short time, it is washed off 
with a sponge, the impression being communicated 
to the ware. The colour depends on the substance 
employed for taking the figure from the engraving. 
In general, a metallic compound is used, such as one 
of cobalt, which gives a blue. In some kinds of 
earthen ware, the patterns are applied with a hair 
pencil, the paint being composed of a metallic mat- 
ter, mixed with a flux and oily substance, which 
when heated melts, and attaches itself to the ware. 
The compounds of antimony and silver give a yel- 
low and orange, gold a purple, copper a green, 
platinum a whitish, and iron a red, brown, or black 
colour, according to the compound used. 

The biscuit as thus prepared, is very porous, and 
of course unfit for containing fluids ; it is necessary,, 



236 ELEMENTS OP CHEMISTRY. 

therefore, to have it covered with a dense body, or 
glazings as it is called. That commonly used is a 
mixture of flints and white lead, both reduced to 
very fine powder, and made into a thin paste with 
water. Into this the biscuit is dipt, by which it 
receives a coating, the porosity of the ware making 
it adhere. When thus covered, they are heaped up 
on small stands of baked clay, in an oven, and expos- 
ed to heat, sufficient to fuse the glazing, by which it 
unites with the materials of the biscuit, and commu- 
nicates a dense coating, having a fine polish, and 
impervious to water, in which state they are ready 
for the market. 

In some instances, the patterns are imparted to 
the ware after the glazing mixture is applied, but 
before it is fused by the heat. In general, however, 
it is put on before it, as has been described is done 
with the copperplate engraving 

Instead of the common glazing, a metallic coating 
is sometimes given to earthen ware, which makes it 
useful for keeping water for a long time warm, the 
earthen ware being a bad conductor, and by receiv- 
ing the metallic coating, becoming also a bad radia- 
tor, {Seepage 100.) 



METALS. 

The metals, from the earliest times, have been 
objects of very great interest, on account of their 
qualities, and the many useful purposes to which 
they are applied. They have properties peculiar to 
them, by which they are distinguished from other 
bodies. They are of great specific gravity, the 
lightest being six times heavier than water, while 
the heaviest is at least twenty-one times its weight. 
They are very tenacious^ by which they are mallea- 
ble and ductile. By ductility is meant that property 



METALS. 237 

by which they can be drawn out to wire. Wires 
are formed by drawing a rod of metal through coni- 
cal holes in a metallic plate, each hole being smaller 
than the preceding one. By malleability is under- 
stood that quality by which they may be beaten by a 
hammer, or extended by rollers into thin leaves. 

The metals vary much in ductility and malleabil- 
ity 3 some scarcely possessing them, except at a 
certain temperature, while others have them in a 
remarkable degree. Thus a grain of gold, it is said^ 
can be beaten out, so as to cover 56 square inches, and 
an ounce of it may be drawn on silver wire, to the 
length of about 1300 miles. During these pro- 
cesses, they become brittle and liable to break ; but 
this is prevented by heating them to redness, and 
allowing them to cool slowly, as by surrounding 
them by ashes, or by a bad conductor, by which they 
are prepared for undergoing the same process. This 
is called annealing. 

The metals are all good conductors of caloric, and 
they expand more than any other solids, their expan- 
sion being very uniform. By the application of a 
sufficient heat, they melt, but the fusing point is 
very various ; thus mercury continues fluid at - — 40. 
Tin fuses at 442, while platinum requires the most 
intense heat that can be applied. Those which melt 
at a low temperature, may be volatilised and again 
condensed in the cool part of the apparatus, unchang- 
ed in their properties, provided they are excluded 
from the atmosphere. When heated in contact with 
air, they lose their splendour and malleability, be- 
come considerably heavier, and resemble in appear- 
ance an earthy substance. This process, formerly 
called calcination^ is now termed oxidation, because 
it is known to be occasioned by the union of the 
metal with the oxygen of the air, and the product is 
called a calx or oxide. The temperature at which it 
occurs, varies in almost every oiflerent instance. In 
some it goes on siovviy,in others with great rapidity. 



238 ELEMENTS OP CHEMISTRY. 

In some it is accompanied with a slight glow, but in 
others it puts on the appearance of combustion, of 
which we have a good example in zinc. To oxidate 
it, we have merely to put it in a ladle, and pkce it 
on a fire. It at first melts, but on continuing the 
heat, and stirring the melted metal, it begins to burn 
with a feeble flame; but when the heat becomes 
more intense, the combustion is very brilliant, and 
a white flaky matter is wafted up, while an earthy 
looking substance remains in the vessel. These are 
the products of the action, a compound of zinc and 
oxygen. It is evident, that since this process de- 
pends on a union of the metal with oxygen, it must 
become heavier, while at the same time the air must 
be diminished ; and that this is actually the case, has 
been satisfactorily proved. If a piece of copper, 
after being weighed, be kept in a fire for some time, 
and again weighed, it will be found considerably- 
heavier ; but, for the success of this experiment, it 
is necessary, on removing it from the fire, to put it 
on a plate, and cover it with a shade till it cools, 
because scales fly oQ", which lessens its weight. 

When a metal is heated in oxygen gas, the com- 
bustion becomes very brilliant, and it can be shewn, 
at the same time, that the gas is consumed, 
this purpose, into a jar of the gas, «, 
open at both ends, and standing on a 
plate of water, 6, introduce at c, a coil 
of very fine iron wire, the end of which 
being tipt with sulphur, is previously 
kindled. It instantly becomes red hot, 
and is gradually consumed, emitting a 
bright white light ; at the same time, , 

if the cork to which is fixed at c, is j Wr^^^^ 
tight, the water will rise, and fill the jar.~~G-lobules 
of a black substance are found in the plate, which 
are the iron in union with oxygen ; and that they 
are so, is proved by heating them in a retort along 
with charcoal, by which carbonic acid gas (a com« 




METALS. 239 

pound of carbon and oxygen) is given oflf, and metal- 
lic iron is left. The calxes, or more properly speak- 
ing the oxides, have in general the appearance of an 
earthy body, though some of them still retain a little 
of the metallic splendour; they are not inflammable, 
and they do not melt so easily as the metals of which 
they are formed. When a metal has been oxidated, 
it may be restored to its metallic state, in some cases 
by the mere application of heat, in others by heating 
them with coal or charcoal, which, as has been men^ 
tioned with respect to that of iron, deprives them of 
their oxygen, tp form carbonic acid, that is given off 
in gas. This is called reduction, and the matter 
subjected to the process is said to be reduced. 

Carbon combines with some of the metals, with 
which it forms interesting compounds. Thus, when 
iron is heated, surrounded by powder of charcoal, it 
is converted into sleeL 

The metals also unite with sulphur ; the union 
may be efiected by melting them together, and the 
appearance presented during their union is remarka- 
ble. Thus, if about equal bulks of iron filings and 
flowers of sulphur be heated in a Florence oil flask, 
over a lamp or chaufier, when the sulphur is properly 
melted, a beautiful glow is at first observed over the 
whole of the mixture, which, in the course of a short 
time, becomes red hot, and continues so for some 
minutes. The compounds formed in this way are 
called sulphurefs, as being compounds of the metals 
and sulphur ; but they are better known by the name 
of pyrites, as iron pyrites, and are very abundant 
productions of nature. They retain some of the 
metallic properties. They have in general considera- 
ble splendour, but they are not malleable nor ductile. 
Many of them are decomposed merely by the appli- 
cation of a strong heat, provided they are excluded 
from the air, by which the sulphur is driven ofl' in 
vapour. Many of the metals are found in the state 
of pyrites, and from these they are procured. 



240 ELEMENTS OF CHiiMISTRY. 

The acids, in general, act easily with metals, the 
action being accompanied with effervescence, or the 
disengagement of a gas, but which varies according 
to the acid, and its state of concentration. With 
some acids, as sulphuric, there is no action at a natu- 
ral heat, unless it is diluted ; hence it is necessary 
in many cases to add water, to cause an action to 
commence. If, for instance, a piece of zinc be put 
into strong oil of vitriol, there is no action ; but, on 
adding water, there is an instant effervescence, and 
disengagement of hydrogen, so that the water is 
decomposed; it gives its oxygen to the metal, and 
its other ingredient, hydrogen, is set free. In other 
cases, as when nitric acid, either pure or diluted, is 
used, the metal acquires oxygen from the acid. Thus 
when a piece of tinfoil, or some iron filings, are 
thrown into it, there is a violent action, and the dis- 
engagement of some of the ingredients of the acid, a 
part of its oxygen combining with the metal. In 
those instances in which an acid dissolves a metal, a 
metallic salt is formed, and which is a compound of 
the acid and m,etal in u7iion with oxygen ; for in 
every instance the metal must acquire oxygen, before 
it unites with the acid, taking it either from the acid 
itself, or from the water with which it is diluted. 
The metallic salts are generally procured in the form 
of crystals, but they differ much from each other in 
appearance ; some being colourless, others of different 
colours. Thus, those of iron are generally green, 
of copper blue, of zinc and lead colourless. 

The names of the metallic salts are composed of 
those of the metal and acid they contain, as is done 
with the alkalies and earths. Thus, that of iron and 
sulphuric acid, is sulphate of iron ^ of lead and mu- 
riatic acid, muriate of lead. It must be kept in 
mind, however, that though these are called sulphates 
or muriates of the metals, they are sulphates or muri- 
ates of the oxides of the metals, for, as it has been 
already said, the acids do not unite with the metals, 
but with the oxides. 



ALLOYS. 241 

Metallic salts are decomposed by the alkalies and 
earths, which combine with their acid, and throw 
down the oxide. Thus, if potassa be added to a solu- 
tion of green vitriol, which is a sulphate of iron, it 
unites with the acid, and oxide of iron is deposited. 

Many of the metallic salts are decomposed by the 
metals themselves. Thus, when a plate of iron is 
introduced into a solution of blue vitriol, which is a 
sulphate of copper, copper in its metallic state is 
deposited, and adheres to the iron. The same hap- 
pens in many other instances, the metal previously 
in solution being deposited, while that introduced is 
dissolved. 

The cause of this difference in the decomposition 
of the metallic salts, depends on the difference in the 
composition of the substances employed. Thus, in 
the first instance, potassa, being an oxide of a metal^ 
unites with the acid, while the other oxide is deposit- 
ed. In the other, the iron, being metallic, before 
it will unite with the acid, must acquire oxygen, 
which it gets from the oxide of copper, and hence the 
copper is deposited in the state of metal. 

Metals have no action with the earths, but their 
oxides combine w^ith them, and form glasses of differ- 
ent colours, and hence their use in imitating some of 
the gems. 

Metals unite with each other, and form a very 
interesting class of substances called alloys, with the 
exception of those containing mercury, which are 
termed amalgams. Alloys retain the metallic pro- 
perties, and are in general more easily oxidated, or 
affected by exposure to heat and air, than the metals 
which exist in them, though this is not always the 
case. The arts of gilding and silvering, and the 
making of brass, pewter, &c. depend on the union of 
one metal with another. 

Metals are found in various states, generally in 
veins or seams penetrating rocks, either in what is 
called their native form, that is, metallic, or in union 
21 



242 ELEMENTS OF CHEMISTRY. 

with some other substance, usually sulphur. In this 
last state they are termed ores, from which they are 
usually procured by different processes, according to 
the metal, and the body with which it is combined. 
In general, the ore is first separated by mechanical 
means from its stony impurities, after which it is 
roasted, and again subjected to heat, with coal or 
charcoal, by which the metal is melted, and falls, in 
its liquid state, to the bottom of the furnace. If it 
be one that is volatile, it is obtained by being sub- 
limed from its ore, and condensed in a cold receiver. 
The process of extracting metals from their ores is 
called reductioa or smelting ; the methods practised 
in the different cases will be noticed, when describ- 
ing the properties of the metals. 

IRON. 

Iro/i is by far the most abundant and useful of 
the metals. It has been long known and in use 
since the earliest ages. When pure, it is of a bluish 
white colour, has a fibrous texture, and, when polish- 
ed, considerable lustre. It is superior in hardness 
to any of the other metals, and is also very malleable 
and ductile It can be drawn to wire of the thick- 
ness of a human hair, the tenacity of which is con- 
siderable. One of the y^sth of an inch, will sustain 
a weight of about 550 pounds without breaking. In 
drawing iron into wire, by passing it through holes 
in well tempered plates, it is usually immersed in 
w-eak aquafortis, merely to clean it. It is said, how- 
ever, to be much better, to put it into a weak solution 
of sulphate of copper or blue vitriol, by which it 
acquires a very thin coating of copper, which pre- 
vents it from being injured by the plate ; the copper 
being easily destroyed by the last annealing, to which 
of course it is frequently subjected during the process. 

Iron is one of those substances which, by the 
application of heat, passes through different degrees 
of hardness. When heated to whiteness, it becomes 



IRON. 243 

soft, and very malleable, so that it is easily wrought 
into different forms. In this state, also, it is easily 
welded^ that is, if two pieces be put together, and 
struck forcibly with a hammer, they unite, and the 
joining is as complete as if it were only one piece. 
The temperature at which this takes place is at about 
a full white heat. When above this, iron becomes 
very brittle, so that it is easily broken ; hence the 
necessity of paying particular attention to the temper- 
ature of the metal. 

When iron is exposed to air, it very soon acquires 
a brown crust on its surface, called rust^ w^hich is a 
compound of the metal and carbonic acid ; but this 
change takes place only when the atmosphere is 
moist, and is owing, therefore, to the decomposition 
of the water, by which the iron acquires oxygen, to 
form an oxide, which oxide combines with the car- 
bonic acid always existing in the air, and thus pro- 
duces a carbonate. 

When iron is heated in air, it unites with its 
oxygen, the facility with which they unite depend- 
ing on the temperature. When made red hot, black 
scales are formed, which are easily detached. If the 
metal be in filings, it is very easily oxidated. We 
have merely to throw a few of these into the flame 
of a sheet of paper, and beautiful sparks are thrown 
off, vvhich are also an oxide. The scales found around 
a blacksmith's anvil, are this oxide, formed during 
the process to which the iron is subjected, and which 
are beat off from it by the hammering. 

Iron acts easily on water, particularly at a high 
temperature ; it combines with its oxygen, and dis- 
engages hydrogen gas. Thus, on applying heat to a 
retort, a^{See p, 167) containing water, and adapted 
to a gun barrel, c, passed through a chauffer, 6, to 
bring it to a red heat, a gaseous fluid is given off, and 
may be collected in the jar, e. Vv'hen heat is appli- 
ed to this, it burns, and during its combustion gene- 
rates water; it is therefore hydrogen. The tube 



244 ELEMENTS OF CHEMISTRT. 

soon loses, however, its power of setting free this 
gas, because its inside becomes lined with a dark 
substance, similar to the scales of iron, and which is 
of course an oxide. Hence, if w^e wish to keep up 
the action, with the view of preparing hydrogen, 
the tube ought to be stuffed with iron shavings. 

Iron combines very easily with carbon, and forms 
the well known substance steeL When extracted 
from its ores, it unites with a little of the carbona- 
ceous matter employed in the process, and forms ca^/ 
iron^ of which there are different kinds according to 
the quantity of carbon. When thin bars of iron are 
kept at a red heat for some time, imbedded in char- 
coal, they unite, and form steel, which is therefore 
d, carburet of iron. Steel is hard and brittle, is of 
a greyish colour, and susceptible of a high polish, 
more fusible than iron, and malleable and ductile. 
Its most remarkable quality, however, is becoming 
very hard, when heated and suddenly cooled. This 
is what is called hardening steel, and the giving it 
the proper degree of hardness, is termed tempeinng. 
When heated in this way, it is the hardest of metals, 
and is also possessed of great elasticity, owing to 
which it is useful in many operations. That steel is 
a compound of iron and carbon, is proved by putting 
a piece of it into diluted nitrous acid, by which the 
former is dissolved, and a black powder is left, hav- 
ing all the properties of the latter. The quantity of 
carbon varies according to the process practised in 
preparing it. In general it is from about 4 to 12 
ounces in the 100 weight. The more it contains, the 
more fusible it becomes ; it is of the utmost conse- 
quence, therefore, to pay particular attention to its 
manufacture. In this country, large troughs are 
built of mason-work, below which fires are placed, 
so as to heat the whole of them. In these are put 
alternate layers of charcoal and bars of iron, and 
when full they are covered with clay. The fires are 
then kindled, and continued for about 10 or 11 days^. 



IRON. 245 

during which the materials are kept at a dull red 
heat. They are extinguished when the iron has 
combined with a sufficient quantity of carbon, which 
is known by taking out a bar, and testing it. From 
the blistered appearance of the article prepared in 
this way, it is called blistered steeL It is used for 
horse shoes, agricultural instruments, and the like. 
When steel is hammered, it is very much improved 
in its properties, and rendered fit for many more 
purposes. This is done by putting together a num- 
ber of pieces of blistered steel, bringing them to a 
red heat, and then hammering them, till they are 
welded, the hammering and welding being repeated 
several times. In this state it is called shear steely 
and is used for making swords, table knives, &c. A 
still finer kind is called cast steel, but difi'erent 
accounts are given of the mode of manufacturing it. 
It is generally said to be prepared by fusing blistered 
steel, surrounded by powder of charcoal and glass. 
According to other statements, it is fused without 
any admixture, and when liquid, poured into moulds, 
and when cold, hammered as in the manufacture of 
shear steel. Cast steel is much closer in its texture, 
and harder, than the other kinds ; hence it is used 
for the finer sorts of instruments, as penknives, 
razors, and surgeon's instruments. 

The acids act very easily with iron, the action 
being different according to the acid and its strength. 
When nitrous acid is poured on it, the action is vio- 
lent, but with sulphuric acid there is none, till it is 
diluted. It is necessary, therefore, to have water, in 
some cases to promote, in others to retard the action. 
In these instances, the iron is dissolved, and forms 
salts, which, as has been already mentioned, {Seep. 
240.) are compounds of acids and metallic oxides. 
By far the most important of these, is that with sul- 
phuric acid. When sulphuric acid, diluted, is pour* 
ed on iron, an action immediately commences, 
accompanied with the disengagement of hvdrogen 
21* 



246 ELEMENTS OF CHEMISTRT, 

2;as; and hence a method of preparing this elastic 
fluid. For this purpose, an ounce and a half of iron 
filings are put into a retort, and on them is poured 
two ounces of sulphuric acid, and eight of water* 
The gas comes off quickly, and may be collected in 
jars. In this instance, the oxygen of the water 
unites with the iron, to form an oxide, and the hydro- 
gen the other ingredient, is set free. There remains in 
the retort a fluid, which, on evaporation, yields green 
crystals, and which are a compound of the oxide of 
iron and sulphuric acid, called sulphate of iron ^ but 
better known by the names of copperas and green 
vitrioly the latter term applied to it from its vitreous 
or glassy appearance. 

Green vitriol is not, however, prepared in this 
way for use. In many places there exists, in large 
quantity, a soft rocky matter, which is a compound 
of sulphur and iron, and which, when exposed to air, 
absorbs oxygen, and is converted into sulphate, the 
sulphur, by its union with oxygen, forming sulphu- 
ric acid, and the iron an oxide, and hence a method 
of procuring green vitriol. For this purpose, the 
substance is collected into a heap, and moistened, 
being frequently turned to expose a fresh surface to 
the air. By washing it and filtering the solution,^ 
crystals are procured. The ease with which sulphur 
and iron, when moistened, abstract oxygen from the 
air, aflbrds also a means of procuring nitrogen gas» 
{See page 142.) 

When green vitriol is subjected to a strong heat, 
it is decomposed, and its acid expelled, but at the 
same time the iron acquires more oxygen from a part 
of the acid. If the heat be continued till the whole 
of the acid vapours come ofi", a reddish powder is left 
in the vessel, called colcothar^ and which is the iron 
in union with oxygen. It is used, when in very 
fine powder, for polishing metals, and for making 
razor straps. As green vitriol is so easily decompos- 
jgd by heat, it affords a method of preparing sulphu- 



INK. 247 

ric acid ; indeed it is that commonly practised on 
the continent, and hence the name oil of vitrioL 
For this purpose, the salt, after being dried by th^ 
application of a slight heat, is put into large retorts, 
having receivers adapted to ihem, and kept cold. 
Heat is applied and continued as long as vapours 
come off, which are condensed in the receiver. There 
remains in the retort, a red powder, which is colco- 
thar ; hence, by this process, two useful substances 
are procured. 

Sulphate of iron, or green vitriol, has the property 
of striking a black colour with the infusion of vege- 
table astiin;:ent matter, as oak bark, Dutgalls, tea, 
and many others, a property common to ail the salts 
of iron. Thus, if a solution of green vitriol be mix- 
ed with the infusion of any of the above substances, 
they either acquire a dark colour, or throw down a 
black precipitate, according to their strength, which 
is a compound of the astringent principle of the veg- 
etable, and the oxide of iron. This property of iron 
is applied to the purposes of dyeings (which see) ; 
it is also valuable as affording a means of making 
tvriting it^k. other substances being added, to impart 
particular qualities. Thus, gum arabic makes it 
more consistent, keeping the black matter suspend- 
ed, and also preventing the ink from spreading on 
the paper, and sugar, or sugar candy, gives it a gloss. 
Logwood, it is said, renders the colour darker, a 
property also possessed by the salts of copper ; and 
by some vinegar is also employed, either alone or 
mixed with water. The use of these two last ingre- 
dients is, however, attended with considerable incon- 
venience, the former acting on the knife with which 
the pen is cut, provided it is not quite clean, and 
thus destroying its edge, vvhile the latter softens the 
quill, and causes it to require to have the nib fre- 
quently renewed. 

The different receipts for making ink very nearly 
agree with each other \ they differ only in the pro^ 



248 ELEMENTS OF CHEMISTRY* 

portions of the ingredients. Perhaps the simplest 
recipe is the following. Put into a bottle three 
ounces of nutgalls bruised, two ounces of logwood 
bruised, one ounce of green vitriol, an ounce of gum 
arabic, and a quart of water. The bottle ought to 
be kept loosely corked for about a fortnight, and 
frequently shaken, after which the cork must be 
tightened. A much better ink is prepared by the 
following. In six quarts beer measure of water, boil 
four ounces of Campeachy logwood for about an hour, 
adding occasionally a little water to compensate for 
loss by evaporation ; strain while hot, and when cold, 
make up the quantity to 5 quarts, then add 20 ounces 
nutgalls bruised, green vitriol dried in an iron ladle 
over a fire to whiteness, 4 ounces ; coarse brown 
sugar, 3 ounces ; gum-arabic 6 ounces, (or for less 
glossy ink half the quantity.) The whole must be 
well mixed and shaken twice a day during fourteen 
days, keeping the vessel loosely corked, to admit the 
air to act on the iron, and make the ink darker. 
After this the impurities are allowed to subside, and 
the fluid poured off. 

Ink is very apt to become mouldy, to prevent 
which, a few cloves, or a few drops of any essential 
oil, as that of peppermint, may be added. The 
greatest imperfections, however, of ink, are its fading 
when long kept, and being destroyed by acids. 
When the writing has faded, it may be recalled, by 
sponging the paper with an infusion of nutgalls, by 
which the traces again appear, the cause of their 
having faded being the destruction of the vegetable 
matter in the ink, by which the iron is still left on 
the paper, and is of course acted on by the nutgalls, 
when the paper is sponged with it. 

Another method of recalling the characters, is by 
sponging the paper with a weak solution of the sub- 
stance called prussiale of potassa^ and afterwards 
with very much diluted muriatic acid, by which they 
acquire a fine blue colour. 



ii^ 



PRUSSIAN BLtJE. 249 

Ink is also easily destroyed by an acid, and that it 
is so is shewn, by putting a little on writing:, or by 
adding a few drops to the dark fluid formed by the 
addition of the astrinsjent matter to the solution of 
green vitriol. If, however, any alkali be added, 
which will combine with the acid, the colour returns; 
hence, if u^riting be destroyed by acids, it may be 
recalled, if the texture of the paper is not injured, 
by sponging it with a weak solution of alkali, and 
for this purpose, the salt called carbonate of ammo- 
nia, or smelling salts, is preferable, as it does not 
act on the paper. 

Chlorine also destroys ink. If the traces have 
been banished by it, they may be recalled, by rub- 
bing the paper over with a weak solution of potassa, 
which has been boiled for some time on flowers of 
sulphur. 

Other kinds of ink are used, when there is any 
danger of the writing being exposed to substances 
that may injure it, the most common of which is that 
with charcoal, prepared by a process formerly men- 
tioned, by holding a plate over the flame of a lamp. 
It is mixed with a solution of gum or isinglass, so 
as to make it of the proper consistence. (See 
page 155,) 

It has been mentioned, that when ink has faded, it 
may be recalled by the substance called prussiate of 
potassa. This is prepared by burning together bul- 
lock^s blood and potassa, washing the residue, and 
after filtration, evaporating, so as to procure crystals. 
This is another very valuable property possessed by 
the salts of iron, as it aflbrds a beautiful paint, called 
Prussian blue^ the manufacture of which has created 
considerable interest. 

A Prussian Chemist, when making experiments on 
iron, had added a solution of one of its salts to that 
of potassa which had been kept for some time on 
animal matter, and found that a blue substance was 
formed. This induced him to make experiments on 



250 ELEMENTS OP CHEMISTRY. 

the subject, b}^ which he discovered a good method 
of preparing the article, which has now received the 
name of Prussian Blue. For preparing it, four parts 
of bullock^s blood, dried by the application of a slight 
heat, are mixed with an equal weight of potassa, 
and again exposed to a strong heat, till the fumes, 
which are first given off, cease to appear. The resi- 
due is then boiled in about twelve parts of water, 
and strained, and to the solution is added two parts 
of green vitriol, and eight of alum, by which a blue 
powder is produced, and is to be washed by muriatic 
acid, and then dried. In the preparation of this sub- 
stance, the blood, by its decomposition, forms an 
acid, that unites with the potassa, by which, when 
the salt of iron is added, the iron and acid unite to 
form the Prussian blue. The use of the alum is to 
combine with it, and thus render it fitter for many 
of the purposes of painters, and the muriatic acid is 
merely to wash away the impurities. 

The methods practised for procuring iron from its 
ores, are nearly the same in all places ; the substances 
used in the reduction, are coke and charcoal; the 
latter is preferred, but, from its scarcity in this 
country, is not much used. The first process to 
which the ironstone is submitted, is to break it to 
small pieces, and roast it, by which the sulphur and 
carbonic acid are expelled, and the iron is left in 
union with oxygen ; it is then reduced, by mixing 
it with coke and lime, and subjecting it to a strong 
heat in a furnace, by which the charcoal unites with 
the oxygen to form carbonic acid, which is disengag- 
ed, and the iron is left in a metallic state; the lime 
acting on the earthy impurities of the ore, and promot- 
ing fusion. When the iron is completely deprived 
of its oxygen, it falls in its fluid form through the 
mxiture, to the bottom of the furnace, and is then run 
off into cavities made in sand, {orming pig iron; and 
it is in this state also, that it is drawn off into moulds, 
forming the different articles of cast iro?i. As cast 



COPPER. 2^51 

iron is very brittle, it is unfit for many of the purposes 
for which the pure metal is employed ; it is therefore 
subjected to the process of refining, which consists 
in exposing it to a strong heat, by which it is melt- 
ed, and when cold, subjecting it to hammerings to 
free it from impurities. These processes of fusing 
and hammering are repeated several times, by which 
the whole of the carbonaceous matter it contained is 
expelled, and it is thus converted into bar or m^alle- 
able iron. 

COPPER. 

Copper has been longer known than any of the 
metals. Before iron was used, it was employed in 
the manufacture of various articles. It is of a red- 
dish colour, has considerable lustre, and acquires by 
friction a peculiar odour. It has also considerable 
malleability and ductility. A wire of the Jgth part 
of an inch in thickness, will sustain a weight of about 
300 pounds without breaking. 

When copper is heated in close vessels, to about 
30 of Wedgewood, that is, about 4970 of F. it melts, 
and its surface becomes of a fine green colour. When 
it is heated slightly in contact with air, it is tarnish- 
ed, and acquires different colours, according to the 
continuance of the heat. If it be kept for some time 
red hot, a dark brown crust is formed, which scales 
off, and is supplied by another. If the metal be 
highly polished, and heated, it assumes various col- 
ours, according to the time that the heat is applied. 
It at first becomes blue, then yellow, and afterwards 
violet. In these different states it is employed for 
ornamenting toys. When copper is subjected to a 
very intense heat, as when exposed to the oxy-hydro- 
gen blow-pipe, it burns with a green flame. 

Copper differs from iron in not decomposing 
water; even at a red heat it has no action w^ith it. 

The acids act very easily with copper, and form 
salts, which are of a blue or greenish colour. By 



&52 ELEMENTS OF CHEMISTRY. 

far the most interesting of these, is that with sul- 
phuric acirl, ihe sulphate^ better known by the name 
of blue vitriol. Though sulphuric acid can dissolve 
<5opper, the sulphate is not prepared in this way ; it 
is always procured by a process similar to that by 
which green vitriol is manufactured, by exposing 
the natural ores containing sulphur and copper to air, 
after being moistened, by which both absorb oxygen, 
the one to become sulphuric acid, and the other 
oxide of copper, and which unite to produce the sul- 
phate or blue vitriol. After it has been exposed to 
air for some time, the residue is washed, the solution 
filtered and evaporated, by which crystals are pro- 
duced. As thus obtained, it is of a fine blue colour, 
having a disagreeable taste ; when exposed to air, it 
acquires a whitish crust on its surface, from its losing 
its water of crystallization. It is soluble in water, 
forming a solution of a blue colour, and which is 
easily decomposed by the alkalies, the action with 
ammonia being peculiar. If to its solution a few 
drops of the solution of ammonia be added, a blue 
powder is thrown down, which is the oxide of cop- 
per; but if more alkali be put in, the powder is 
dissolved, and the fluid becomes transparent, and of 
a fine blue colour. This is the fluid so frequently- 
seen in the windows of apothecaries' shops. 

Blue vitriol, it has been already observed, is em- 
ployed by some manufacturers of ink, to make the 
colour darker, and it is used also by dyers, for strik- 
ing diflerent colours. 

Iron throws down copper from a solution of any 
of its salts. Thus, w^hen a plate of iron is put into a 
solution of blue vitriol, it is very soon covered with 
a thin coating of copper. Here the iron decomposes 
the salt of copper ; it takes the oxygen from it, by 
which it is converted to an oxide, and unites with the 
acid, so that the copper, being brought to its metallic 
state, is deposited. 



COPPER. 253 

Copper combines with other metals, as with zinc 
and tin, with the former of which it forms brass, 
and with the latter pewter. {See Zinc and Tin.) 

Copper is not an abundant production. It is found 
occasionally, though rarely, in its metallic state. In 
general, it is in union with oxygen or sulphur, and 
sometimes also with other metals. The ore from 
which it is chiefly obtained, is the sulphuret, a com- 
pound, as the name shews, of sulphur and copper, 
and which is found principally in Cornwall, Angle- 
sea, and Hungary. In procuring it from this, it is 
first broken to small pieces, and roasted, to drive off 
the sulphur and arsenic, which it frequently also 
contains. It is then put into a furnace and melted, 
being occasionally mixed with a little lime, to in- 
crease the fusibility, and when fluid, it is drawn off 
through a hole in the bottom of the furnace, and put 
into water, by which it is gramdated^ or reduced 
to coarse powder. The copper thus obtained, is kept 
at a low red heat for some days, and is, after this, 
repeatedly fused and cast into moulds, and lastly, it 
is placed in a refining furnace with a little charcoal, 
and again melted, after which, if it bear hammering, 
it is fit for sale. The very thin sheets of copper 
employed in the arts, are prepared by allowing the 
melted metal to cool to very near its congealing 
point, and then drawing a wet broom across it, by 
which the surface is consolidated, forming a thin 
plate. When this is done, it is removed, and instant- 
ly plunged into cold water, by which it assumes a 
fine red colour. Copper, in a state of considerable 
purity, is occasionally procured also from waters 
which contain it. For this purpose, pieces of iron 
are thrown in, and left there for some time, by which 
they are dissolved, and the copper deposited in their 
place, so that they appear to be converted into cop- 
per, the action being here the same as that already 
noticed, the iron taking oxygen from the copper, 
and combining with its acid to form a soluble com- 
22 



254 ELEMENTS OP CHEMISTRY. 

pound, while the copper in its metallic state is de- 
posited. 

LEAD. 

Lead has been long known. It is of a pale bluish 
colour when recently cut, but very soon tarnishes 
by exposure to air. It emits a particular odour when 
rubbedj and leaves a dark stain on paper. It is one 
of the softest and least malleable of the metals, and 
is far inferior in malleability, ductility, and tenacity, 
to iron and copper. When subjected to a tempera- 
ture of about 612, it fuses ; and if the heat be raised 
much higher, it is sublimed. It is one of those metals 
which are easily oxidated by heat and air. When 
kept at a high temperature, it loses its lustre, and 
acquires a crust on its surface, and at last a white 
powder is formed. By removing this, or by stirring, 
the whole is converted to a greenish substance, which 
is a mixture of oxide with minute particles of metal ; 
but by subjecting it to heat and air, a yellow powder 
is formed, which is a pure oxide, and sold under the 
name of massicot. When this, ground to powder, 
is kept at a strong heat, the flame of the coals at the 
same time playing on it, it becomes red, forming 
Tnmiunij or red lead^ and which, when heated sud- 
denly, and a current of air being allowed to pass along 
it,undergoes asort of fusion, and becomes whatis call- 
ed litharge. All of these are compounds of lead and 
oxygen, the lead having acquired the oxygen from 
the air. 

The oxides of lead are not decomposed by heat 
alone ; they require the presence of inflammable 
matter. Thus, when heated with charcoal, it com- 
bines with their oxygen, and the lead is brought to 
its metallic state. 

Lead has no action with water when pure ; but 
when it is wetted and exposed to air, it undergoes 
oxidation. When kept also in water that is not pure, 
it suffers a change ; a white crust is formed on it. 



LEAD. 255 

which is a carbonate, the carbonic acid being deriv- 
ed from some of the substances in the water. This 
is one of the most important of the compounds of 
lead and the acids ; it is white leadj or cerusse, 
employed by painters in making oil paints. White 
lead is prepared by first casting the metal into thin 
sheets, which are coiled up, and put into vessels 
similar to flower-pots. Into these vinegar is poured, 
till it reaches near the lower part of the metal ; after 
which the pot is covered, and placed in horse dung, 
or tanners' bark, and kept there for several weeks. 
By the heat generated by the bark or dung, the vin- 
egar is converted to vapour, and, acting on the metal, 
forms a white crust, which is removed by passing 
the plates between rollers, or by moving them back- 
wards and forwards in water, by which the dust is 
prevented from rising, and proving injurious to the 
workmen. The white lead thus prepared is subject- 
ed to the action of water, by which the finer is sepa- 
rated from the coarser part. In this process, the 
vinegar, which is a compound of carbon, oxygen, 
and hydrogen, is decomposed ; it gives oxygen to 
-the lead, to convert it to an oxide, while a part of the 
carbon and oxygen unite, to form carbonic acid, 
which combines with the oxide, thus forming the car- 
bonate, or white lead. 

Another important compound of lead, is that with 
muriatic acid, the muriate^ or what is commonly 
called Turner^ s yelloiv^ which is prepared in one of 
the processes followed for decomposing sea salt, to 
make it yield its soda. 

When sea salt is made into a paste with litharge, 
it is decomposed, its acid unites with the litharge, 
and the soda is set free. Hence the patent process 
of Turner for decomposing sea salt, which consists 
in mixing two parts of the former with one of the 
latter, moistening them, and leaving them together 
for about 24 hours. The product is then washed 
with water^ filtered, and evaporated, by which soda 



256 ELEMENTS OF CHEMISTRY, 

is obtained. A white substance is left undissolved; 
it is a compound of muriatic acid and lead, which, 
when heated, changes its colour, forming Turner^s 
yellow, employed as a paint. 

Lead unites with vinegar, or rather with the acid 
in it, and forms the well known substance, sugar 
of lead ^ called by chemists acetate oflead, because 
the acid in it is termed acetic. It may be prepared 
by dissolving white lead in vinegar, but it is usually 
procured by exposing the m.etal to the action of the 
fluid. It has been already mentioned, that white lead 
is prepared in this way. If that part of the metal 
covered with the crust be put into the vinegar, it is 
decomposed, the carbonic acid is driven off, and the 
acid unites with the lead. When the surface is 
cleaned, another part is put in, by which the crust 
on it is removed, and the other again acquires a crust, 
so that, by putting in alternately different parts of 
the lead, the whole of it is combined with the acid 
of the vinegar. A solution is thus procured, which^ 
when filtered and evaporated, yields acetate, or sugar 
of lead, so called from its sweetness. As thus obtain- 
ed, it is like loaf sugar. It is soluble in water, but 
the solutinon is opake, owing to the action of carbonic 
acid, that always exists in water, forming with it a 
little white lead. From this it is easily freed by the 
addition of a few drops of vinegar, or aquafortis, 
which converts the white lead into a soluble salt. 

Hence also the cause of the turbidity on mixing a 
solution of sugar of lead with water. 

Sugar of lead is employed chiefly by dyers and 
calico-printers in the preparation of some of their 
7nordants^ or those substances which they use for 
fixing colour on cloth. One of these is acetate of 
iron, which is procured by mixing equal parts of 
sugar of lead and green vitriol, previously dissolved 
separately in water, by which there is a double decom- 
position ; the sulphuric acid uniting with the lead, 
and the acetic acid with the iron. The former is 



TIN. 257 

insoluble, and is precipitated i the latter is held in 
solution, and may be separated by filtration. 

The oxides of lead form excellent fluxes with earthy 
matter ; he ice they are used for causing them to 
melt more easily. Thus, litharge is employed in 
the manufacture of glass, by which the materials are 
more easily fused, and the glass acquires a greater 
lustre {See page 231.) When the litharge is in 
large quantity, it makes the glass yellow. White lead 
is employed, when mixed with powdered^ flints, and 
sometimes also with sea salt, as a glazing for stone- 
ware. (See page 236 ) 

Lead, in its metallic state, is employed in thin 
sheets for covering the tops of houses, and in finer 
plates for lining the inside of boxes, and for covering 
the mouths of bottles in which volatile fluids are 
kept, the bottle being first covered with bladder, 
then with sheet lead, and again with bladder. 

Lead is an abundant production of nature. The 
ore from which it is usually procured is a compound 
with sulphur, the sulphuret^ or what is commonly 
called galena^ and which is easily reduced by heat 
alone. For this purpose, after being freed from its 
stony impurities, it is placed in a furnace, and made 
quickly red hot, being frequently stirred ; and when 
it begins to soften, the heat is reduced, till the whole 
of the sulphur is expelled. The fire is then made 
brisk, by w^hich the lead is melted, and collects at 
the bottom of the furnace ; after which, lime is 
thrown in, to thicken the impurities that collect on 
the surface, and the fused metal is drawn off into 
oblong moulds. 

Lead ore frequently contains a suflScient quantity 
of silver !o make it of consequence to extract it from 
it. {Set Silver,) 

TIN. 

Tin has been long known. It is of a whitish 
colour; with considerable lustre, having somewhat 

22^ 



258 ilLEMENTS OF CHEMISTRY. 

the appearance of silver. It is very malleable^ being 
easily beaten into leaves which are only about foVo^h 
part of an inch in thickness. Common tinfoil is of 
this thickness, but finer leaf can also be prepared. It 
is not possessed of much ductility, nor is it very 
tenaciousj a wire of the 10th part of an inch sustain- 
ing a weight of only about 50 pounds. It has but 
little elasticity, and in bending emits a crackling 
noise. It is so soft, as to be easily cut. When ex- 
posed to air, it tarnishes, though slowly. When 
heated, it melts at 442, and if the heat be continued, 
it acquires a w^hite crust on its surface, which soon 
becomes yellow ; and if the temperature be high, and 
a stream of air be passed over it, it takes fire, and 
forms an oxide. This is easily shewn, by melting it 
in a ladle, and blowing on it, taking care to keep up 
the heat. 

The acids act very easily with tin. Thus, when 
a piece of tinfoil is thrown into nitrous acid, the 
action is violent, and a white powder is formed, 
which is an oxide, the metal having taken oxygen 
from the acid. If w^e w^ish to dissolve the tin, it 
is necessary to dilute the acid, and allow the action 
to go on slowly. The most important salt of tin is 
that with muriatic acid. This acid acts feebly on it, 
but the action is promoted by heal, and a transpar- 
ent colourless solution is formed ; the water in the 
acid giving oxygen to the metal, to form an oxide, 
which unites with the acid, forming muriate of tin. 
The action between tin and aqua regia is also inter- 
esting. When put into it, it is dissolved, and a solu- 
tion of inuriate is formed. Both of these are 
employed by dyers as mordants, and also for afibrding 
a rich red colour with some dye stuffs. A cheap 
solution of tin for the same purpose, is prepared by 
dissolving 14 ounces of it in a mixture of 3 pounds 
of muriatic and 1 of sulphuric acid. Muriate of tin 
undergoes a change when exposed to air ; it absorbs 
oxygen, and is thus better fitted for striking a red 



TIN. 259 

f:olour. Hence its use in making red ink. To 
make red ink, boil 1 lb. of chips of Brazil logwood in 
three quarts of water, for half an hour ; strain the 
decoction, and evaporate to a pint (English), then 
add half an ounce of solution of muriate of tin which 
has been exposed to the air, half an ounce of spirit of 
wine, a quarter of an ounce of muriatic acid, and 
a quarter of an ounce of brown sugar. Muriate of 
tin, for this purpose, is prepared, by dissolving tinfoii 
in muriatic acid, keeping the flask near a fire to pro- 
mote the action. 

Tin unites with the greater number of metals, w^ith 
some of which it forms very important alloys. It 
does not combine very easily with iron, but they 
can be made to enter into union, by melting them in 
a covered crucible. Tinning of iron depends on the 
attraction exerted between them. Tinned iron^ or 
white iron^ as it is commonly called, and sometimes, 
but improperly, tin, is formed, by dipping very thin 
sheets of iron into melted tin, previously mixed with 
about yVth part of copper, which prevents too much 
of it from adhering to the iron, and having its surface 
covered with tallow, to preventoxidation, at the high 
temperature to which it is exposed. In this process, 
the iron seems to be penetrated by the tin, for the 
whole of it acquires a white colour. 

Tinned iron is a very useful alloy ; it does not 
easily rust, besides, the elasticity of the iron is not 
much impaired, and, owing to the fusibility of the 
tin on its surface, two pieces of it are easily soldered 
together. 

Pots are often lined with a thin layer of tin, which 
is done by first rubbing over their surfaces with sal 
ammoniac, and after heating them, pouring in some 
melted tin, and revolving them, so that the whole of 
it may be brought in contact with the iron, by which 
it acquires a coating, that prevents it from undergo- 
ing any change by exposure to air. Perhaps the 
alloys of tin and copper are the most useful. Tin 



260 ELEMENTS OF CHEMISTRY. 

diminishes the ductility, but increases the hardness 
and tenacity of copper, and it also renders it more 
sonorous, and more easily fused. To procure an 
alloy in the proportion in which the metals are mix- 
ed, it is necessary to keep the mixture long in fusion, 
and to stir it constant!} during cooling. In this way 
are formed bronze, gun urtetaU bell metaU and that 
used for the reflecting mirrors of telescopes. The 
two first are compounds of 100 copper, and from 8 to 
10 of tin. The alloy is yellow, and is more easily 
melted than copper, hence its use in making statues. 
It was used also by the ancients before iron was 
known, for swords, spears, and other warlike instru- 
ments, and many of their sharp edged tools and 
medals are made of it. Bell metal is composed of 
100 of copper, and about 30 of tin, the gong of the 
E. Indians being nearly of the same composition; and 
the metal for telescopes contains a still larger propor- 
tion of tin, about 100 to 50. 

Tin unites with lead in almost every proportion ; 
the alloy is easily fused, hence it is employed as a 
solder ; plumbers' solder being usually composed of 
about equal parts of tin and lead. 

Tin is not an abundant production of nature. It 
is found in but few places, as in Gallicia in Spain, in 
Saxony, Bohemia, and in Cornwall in England. Its 
ores are the sulphuret and oxide, from the latter of 
which it is got by heating it with inflammable mat- 
ter. For this purpose, after being freed as much as 
possible from earthy impurities, it is roasted to drive 
off any sulphur, and then mixed with coal or coke, 
and again subjected to heat, during which the carbon 
unites with the ox3^gen, and the tin, brought to its 
metallic state, is fused, and is drawn off into shallow 
pits. When solid, it is exposed to a moderate heat, 
so as to melt the purest part, which is run off into 
moulds, ad forms ^ram tin. What is left is com- 
mon tin, which is not so pure as the other, contain- 
ing a little copper, iron, and arsenic, 



ZINC. 261 



ZINC. 

Zinc or Spelter^ has not been long known, but one 
of its compounds was used by the ancients in the for- 
mation of brass, of the nature of which^ however, they 
were ignorant. The metal itself seems to have been 
discovered about the middle of the 16th century. 
When pure, it is of a bluish colour, hard and brittle, 
and, when recently broken, of considerable lustre. 
It was formerly considered one of those metals not 
possessed of malleability or ductility, but it is now 
known to have both of these qualities. By cautious 
and equal pressure, it may be extended into plates, and 
by heating it to a certain temperature, its malleability 
and ductility are much increased. The temperature 
at which this takes place, is from 212 to 300. It 
may then be beaten to thin plates, and drawn into fine 
wire, which, when annealed, retains considerable 
tenacity, one of the 10th of an inch in thickness 
sustaining a w^eight of about 2Q lbs. If the zinc be 
heated much beyond the temperature stated, as to 
about 400, it becomes so brittle, that it is easily 
reduced to powder. When heated in close vessels 
to about 680, or 700, it melts, and by a higher tem- 
perature is volatilized. When heated in contact with 
air, it soon acquires a crust on its surface, and if it 
be stirred when in this state, the whole of it is con- 
verted to a white powder, which is an oxide. If the 
temperature be high, it takes fire and burns with a 
bright flame, which becomes more brilliant by blow- 
ing on it, {See page 238). The oxide thus formed is 
white, and cannot be decomposed by heat alone ; it 
requires the presence of inflammable matter, as char- 
coal, and the process must be carried on in vessels 
from w^hich the air is excluded, otherwise the metal, 
vvhen formed, instantly unites with oxygen, and 
again becomes an oxide. 

Oxide of zinc is employed by some painters, instead 
of white lead, in the preparation of their paint. 



262 ELEMENTS OF CHEMISTRY. 

Though it is more troublesome to work with, yet in 
other respects it is preferable to white lead. It is 
not at all liable to become dark coloured, and it does 
not prove injurious to the w^orkmen. 

All the acids act easily on zinc, owing to its power- 
ful attraction for oxygen. The action between it and 
sulphuric acid is interesting, as it affords a method of 
procuring hydrogen in a state of purity, and another 
substance also employed in the arts, sulphate of 
zinc, or white vitriol. For this purpose, having put 
an ounce of zinc into a retort, pour on it an equal 
quantity of oil of vitriol, diluted with five of water. 
Here the oxygen of the w^ater unites with the zinc, 
and the hydrogen is set free ; the oxide then combines 
with the sulphuric acid, to form the sulphate. The 
hydrogen obtained by this process, is much purer 
than that got by iron. It has less unpleasant odour, 
and it is of less specific gravity. By evaporating 
the solution in the retort, crystals are obtained. 
This is the mode by which the purest white vitriol 
is prepared ; but that of commerce is generally pro- 
cured by a process similar to that by which green 
and blue vitriol are formed, by exposing the ore of 
zinc and sulphur to air and moisture, by which both 
combine with oxygen to form sulphuric acid and oxide, 
which unite, and form the sulphate. By washing 
the residuum, filtering, and evaporating, a substance 
is obtained, in its appearance resembling loaf sugar, 
having: a disagreeable taste, and when swallowed, 
almost instantly exciting severe vomiting. It is used 
by dyers for making some of their dj^es more perma- 
nent, as those from madder and cochineal. It is 
sometimes also used for making drying oil. fSee 
OIL) 

Zinc decomposes many of the metallic salts. It 
combines with the acid with which the other metal 
is in union, and forms a soluble compound, while the 
other metal is deposited, the appearance presented be- 
ing very beautiful. The decomposition goes on slowly^ 




BRASS AND PEWTER. 263 

and the metal is deposited in the form of a tree, with 
innumerable branches, as is well exemplified in the 
case of lead. Thus, when a rough piece 
of zinc, is suspended near the top of a 
tall bottle, 6, filled with a solution of sugar 
of lead, rhe latter metal is separated from its 
acid, and attaches itself to the former, and 
each portion, set free after this, adheres to 
that previously disengaged, and thus puts 
on the ramified appearance. The solution 
is prepared, by dissolving one part of sugar 
of lead in tbrty of water, and either adding a few 
drops of vinegar to make it transparent, or filtering 
it. The bottle must be kept without agitation, oth- 
erwise the tree is easily broken. 

Zinc does not occur in its metallic state, nor are its 
ores numerous. It is found chiefly in union with 
sulphur and carbonic acid, in the substances called 
blende and calamine^ from which it is always ob- 
tained. For this purpose, the ore is first roasted, to 
drive oif the sulphur from the former and the carbo- 
nic acid from the latter ; after which it is mixed with 
charcoal, and reduced bv the application of heat. 
The vessels in which the smelting is conducted, are 
large earthen pots, through the bottom of which there 
passes a tube, the upper end of which terminates by 
an opening near the top ; the lower one goes through 
the furnace into water. After they are filled with 
the mixture of ore and charcoal, the lids are put on, 
and heat applied, by which the metal is reduced, and 
converted into vapour, which passes through the 
tube, and is condensed in the water in the form, of 
globules ; these are afterwards melted, and poured 
into moulds. 

Zinc is employed in great quantities in the forma- 
tion of brass, pinchbeck, and pewter, the two first 
of which are alloys of it and copper ; the last is in 
general a compound of copper, lead, tin, and zinc. 
Owing to the low temperature at which zinc is melt- 



264 ELEMENTS OF CHEMISTRY. 

ed, and even volatilized, it is difficult to obtain a 
perfect alloy of it and copper, because, before the 
latter is fused, a great deal of the former is volatiliz- 
ed. There is, however, an easy method of alloying 
copper with zinc, by what is called cementation^ 
which consists in exposing it to heat, along with a 
mixture of zinc ore and charcoal, during which the 
ore is decomposed, zinc is formed, and unites with 
the copper, and converts it to brass. For this pur- 
pose, the ore, after being roasted, is mixed with 
charcoal, and put into large earthen pots with pieces 
of copper, and when the lids are secured, heat is 
applied, sufficient to soften, but not to melt the cop- 
per, as the zinc, when brought to its metallic state, 
will penetrate it; but after the brass is formed, the 
temperature is raised, by which it is melted and 
drawn off into moulds. The proportions of the in- 
gredients of brass vary in different places. In some, 
40 of copper and 60 of zinc ore are employed, w^hich 
yield about 60 of alloy, making the proportions 2 of 
the former to 1 of the latter. It is seldom, however, 
that the quantity of zinc is so high ; in general it 
does not exceed 20 per cent. Brass is more fusible 
than copper, and as malleable when cold. It posses- 
ses, however, one disadvantage, that of being decom- 
posed at a high temperature, for, w^hen kept long 
melted in contact with air, the greater part of the 
zinc is consumed ; so that, in working with brass, 
the temperature ought not to be allowed to approach 
that, at which the zinc will be taken from it. Zinc 
with a larger proportion of copper forms alloys, which 
are employed in making trinkets, 2lS pinchbeck^ tin- 
selj and Dutch leaf. These are generally procured 
by melting brass with an additional quantity of cop- 
per, the proportions varying according to the colour 
required. 

MEKCURY. 

Mercury y or Quicksilver^ is distinguished from 
all other metals, by being fluid at a natural tempera- 



MERGURT. 265 

ture. It is of a bluish white colour, and very re- 
splendent ; but, by exposure to air, it attracts mois- 
ture and dust, which makes its surface dull. This, 
however, is easily restored, by squeezing it through 
a leather bag. So early as the year 1759, it was 
discovered that mercury might be made solid, by 
subjecting it to a very intense cold. The tempera- 
ture at which this takes place is about — 40. It is 
then malleable, and can be easily cut. When mer- 
cury is heated to about 660, it boils, and is convert- 
ed into vapour, which condenses unchanged in its 
properties, in the cool part of the apparatus. By 
this means, we are enabled to free it from the impu- 
rities which it usually contains, as when it is requir- 
ed pure for filling thermometers. For this purpose, 
it is placed in an earthen ware or iron retort, the 
mouth of which terminates in a basin of water. By 
applying heat, the mercurial vapour is given off, and 
condensed in the water, from which it is easily freed, 
by pouring off the fluid, and then passing the mer- 
cury through a tow^el, and keeping it in bottles, so as 
to exclude it from the air. 

Mercury unites with sulphur, and forms compounds 
of different colours ; the only one of any interest is 
the red sulphitret, commonly known by the name 
of cinnabar. It is a natural production, being the 
ore from which mercury is usually obtained, but it 
is also often prepared artificially. For forming it, 
about 90 parts of mercury, and 10 of sulphur, are 
put into an iron pot, and heated, the mixture being 
constantly stirred, till the whole of the metal disap- 
pears. What is left is of a black colour; it is reduc- 
ed to powder, and thrown, in successive portions, 
into earthen pots, previously heated to redness, by 
v;hich a part of it is inflamed, but the flame is instant- 
ly checked by putting on a lid, and the process* is in 
this way carried on, till the w^hole of the material 
is used. The heat is then continued for several 
hours ) during which, part of the mixture sub- 
23 



266 ELEMENTS OP CHEMISTRY. 

limes, and is condensed in the upper part of the 
vessel. 

Cinnabar, as thus prepared, is dark coloured, but 
when reduced to powder, becomes of a rich red 
colour; in which state it is sold under the name of 
Vermillion. 

Most of the acids act on mercury, and form salts, 
few of which, however, are applied to use in the 
arts. Perhaps the most interesting of these, is that 
called corrosive sublimate. As muriatic acid does 
not dissolve mercury, it is necessary to cause them 
to act on each other indirectly. For this purpose, 
the mercury is first dissolved in sulphuric acid, and 
the solution evaporated to dryness; after which the 
residue is mixed with dried sea salt, and exposed to 
heat in ajar, a, having a top, b, fixed to it, 
by which a vapour is given off, that con- 
denses in the cool part of the apparatus. By 
dissolving the mercury in sulphuric acid, a 
sulphate is obtained, a compound of sulphuric 
acid and oxide of mercury ; and when this is 
mixed with sea salt, there is an exchange of 
ingredients, by which the mercury is sublimed in 
union with the muriatic acid. As thus procured, it 
is in white cakes, having a crystalline appearance. 
It is soluble in 20 parts of cold water, forming a solu- 
tion, which is easily decomposed by many of the 
metals, the mercury adhering to the other metal. 
Thus, when a plate of copper is put into a solution 
of corrosive sublimate, it acquires a thin coating of 
mercury. It is owing to the ease with which corro- 
sive sublimate gives off its mercury, that it is employ- 
ed for some sorts of silvering. (See Silver.) 

Mercury unites with most of the metals, and forms 
substances called amalgafris. They are generally 
brittle, and if the mercury be in large quantity, are 
soft, or even fluid. The only amalgam of any use in 
the arts, containing a metal, the properties of which 
have been described, is that with tin. It is the sub- 




MERCURY. 267 

stance employed for silvering the backs of mirrors. 
For this purpose, a sheet of tinfoil is put on a smooth 
table of freestone or hardwood, and a little mercury 
rubbed on it, by means of the finger or a hare's foot, 
till the whole is amalgamated, after which more is 
poured on, till it is about •j^^^'^ ^f ^t"^ ^"^ch in depth. 
The surface is then freed of any impurities, and 
having next laid a sheet of thin paper on it, the plate 
of glass is put over it, and the paper withdrawn, by 
which all air bubbles are removed. A weight is 
then put on, and the stone inclined by a wedge, to 
allow part of the mercury to escape. In the course 
of an hour, more weights are put on, and the stone a 
little more inclined ; and by leaving it in this situa- 
tion for some hours, the wiiole of the superfluous 
mercury is squeezed out. A resplendent coating is 
thus given to the glass, and which adheres to Jt with 
considerable force. 

Mercury is occasionallj'-, though rarely, found in 
its metallic state. It occurs chiefly in union with 
sulphur, in the red sulphuret, or cinnabar, from which 
it is always obtained ; the process for smelting the 
ore differing in different places. 

In Spain, cinnabar is expensed to heat, by which 
the sulphur is burned, and the mercury is obtained 
in its metallic state. For this purpose, it is placed 
in a long horizontal building, divided into an upper 
and under compartment by a grating of iron, on 
which is placed the ore, broken to small pieces, and 
covered with bricks made of the ore and clay. Wood 
is then kindled in the lower compartment, by which 
the moisture of the cinnabar is expelled, and the 
sulphur is inflamed, after which the fire is extinguish- 
ed, the heat generated by the combustion of the 
sulphur being sufficient to drive off the mercury in 
vapour, which is condensed in a receiver, attached 
to the building. The method practised in Germany 
for procuring mercury is different. The finer part 
of the ore being separated from the coarser, it is 



268 ELEMENTS OF CHEMISTRY. 

reduced to powder, and mixed with about Jth of 
its weight of slaked lime, and put into iron retorts, 
each of which holds about half a hundred weight. 
From 40 to 50 of these are built into a furnace, and 
heat applied, by which the mercury is driven off in 
vapour, and condensed in receivers. The quantity 
thus obtained is very small, which makes the process 
an expensive one, 100 lbs. of ore yielding only from 
6 to 10 ounces. 

The principal use of mercury is, amalgamating it 
with other metals, chiefly gold and silver, so as to 
obtain them pure. It is used also in gilding and sil- 
vering, and in making mirrors. Its use in the con- 
struction of thermometers and barometers^ has been 
already explained. 

GOLD. 

Gold has been long known. Its scarcity, and its 
superior metallic properties, render it the most valua- 
ble of the metals. When pure, it is of a reddish 
yellow colour, with considerable lustre, which is not 
liable to be altered by exposure to air. It is soft, but 
is far superior in malleability and ductility to the 
other metals. One grain can be beat to leaves of 
about 2To!o 0^0^ th of an inch in thickness, and will 
cover 56 square inches. By putting gold on silver, 
and drawing it to wire, it may be still further extend- 
ed, for the whole of the silver still retains a coating 
of gold, which is only y^^h part of the thickness of 
the leaf. One grain, it is said, may be in this way 
drawn out to about 2 miles and fths in length. 

The ductility of gold is also very great, being 
easily drawn to wire finer than that of any other 
metal. Its tenacity is also considerable, a wire about 
the yV^h of an inch in thickness bearing a weight of 
150lbs. without breaking. Gold melts at 32 of Wedge- 
wood, (5237 Fahrenheit), and during its fusion, it 
enlarges, consequently it shrinks when it congeals. 
In its liquid state, it is of a bright green colour. 



GOLD. 269 

Gold is one of the metals that are not affected by- 
heat and air. When subjected to a high temperature, 
in contact with air, it does not suffer any change, but 
it can be oxidated by electricity, by which an oxide 
of a purple colour is formed. 

Gold also resists the action of all the acids, except 
the nitro-muriatic or aqua regia ; even nitric acid, 
which acts so very powerfully on metals, does not 
dissolve it. If some gold leaf be put into nitrous 
acid, and into muriatic acid, there is no action } but 
if the fluids, with the gold in them, be mixed, it is 
almost instantly dissolved. The ease with which 
this dissolves it, is supposed to be owing to the pre- 
sence of chlorine, which acts so powerfully on all 
metals. The best proportions are 2 of muriatic, and 
1 of nitrous acid. When gold is put into this, and 
a slight heat is applied, it is dissolved, and should 
any excess of acid be left, it is easily driven off by 
boiling. The solution thus formed, is a muriatey 
the gold having acquired oxygen, and then united 
with the muriatic acid. When to the muriate of 
gold a solution of tin in muriatic acid is added, a 
purple powder is precipitated, commonly called the 
purple poioder of Cassius, For preparing it, tin 
leaf is dissolved in aqua regia, composed of two parts 
of nitric and 1 of muriatic acid, without the applica- 
tion of heat. The solution is then mixed with that 
of the muriate of gold, and the purple powder is 
gradually deposited. It may be obtained also by 
putting a few pieces of tin leaf into the solution of 
gold, and leaving them there for some time, during 
which the powder is formed. This is perhaps the 
best mode of preparing it, as it seems to afford it 
freer from impurities. Different opinions are enter- 
tained with respect to the composition of this pow- 
der. It is generally, however, supposed to contain 
the oxide of both the metals. It is used for making 
red glass, and hence its use in imitating some of the 
gems. Muriate of gold is employed for giving a 
23* 



270 ELEMENTS OF CHEMISTRY. 

coating to other metals, particularly iron. This is 
done by diluting the solution with spirit of wine, and 
putting the iron into it, its surface being previously 
well polished. In the course of a short time, it 
acquires a covering of gold, which may be made to 
adhere firmly by burnishing. Instead of spirit of 
wine, ether is sometimes employed. The solution 
of the muriate being evaporated to dryness, the resi- 
due is dissolved in ether, into which the iron is 
immersed, and almost instantly removed. By expo- 
sure to air the ether evaporates, and leaves the gold 
adhering to the iron, so that, by repeating the process, 
a sufficiently thick coating may be given to it. In 
this way finer sorts of instruments are sometimes 
gilded, more particularly if they are likely to be 
exposed to moisture, and are thus prevented from 
being rusted. Muriate of gold is also employed 
in porcelain painting. For this purpose it is mixed 
with borax and gum, and applied to the ware by 
means of a hair pencil. By the application of heat, 
the part covered with it acquires a rich red colour. 
Gold combines with other metals, and forms useful 
compounds, the most important of which are those 
with copper and mercury. When alloyed with cop- 
per, it acquires the valuable property of becoming 
much harder, owing to which it is mixed with it 
when employed for making coins. From numerous 
experiments it has been ascertained, that the hardest 
alloy is that composed of II of gold, and 1 of copper. 
British Standard or Sterling Gold contains ^V^h 
part of its weight of copper.* Coins made of this are 

* The standard of the gold coins of the U. S- consists of 11 parts of fine gold to 1 
part alloy, which alloy consists of silver and copper in any convenient proportion, 
provided the silver do not exceed the copper. The Eagle of 10 dollars contains 270 
grains of standard gold, of which 247 1-2 grains, are fine gold and 22 1-2 grs. alloy. 
The Troy pound of standard gold contains 11 ounces of fine gold find 1 ounce alloy, and 
is coined into 21 1-3 eagles, of the value of 213 1-3 dollars ; orS ounces of standard 
gold are coined into 16 eagles of the value of 160 dollars. The proportional value 
of fine gold to fine silver by the laws of the U. S. is as 15 to 1 ; so that 1 pound of 
fine gold is worth 15 pounds of fine silver. The proportional value of the different 
gold and silver coins is derived wholly from the proportion of fine gold in the one, to 
the fine silver in the other, the alloy in both being disregarded. Thus, 21 3-4 jrrains 
of fine gold being 1-lOth of the fine gold in our eagle are equivalent to our dollar, and 
multiphed by 15 produce 371 1-4, the grains of fine silver in the dollar. MaTtual.^ 
^agQ 415. 



GOLD. 271 

much harder than those of pure gold ; hence the im- 
pressions on them continue much longer entire. Jew- 
ellers' gold contains much more of the alloying metal, 
and sometimes, instead of copper, a mixture of it and 
silver is used, the latter giving to the compound a 
colour more nearly the same as that of pure gold, 
while copper alone makes it darker. Hence its fre- 
quent use in making trinkets. 

There exists a strong attraction between gold and 
mercury, so that they can be easily amalgamated. 
When a piece of gold is dipt into mercury, it merely 
acquires a white colour ; but, by putting it when red 
hot into the other brought nearly to its boiling point, 
a soft amalgam is formed, from which the superfluous 
mercury can be removed, by squeezing it in a leather 
bag. By this means a substance is obtained, con- 
sisting of about 1 of gold and 2 of mercury, and from 
which the latter is easily driven oflf by heat ; hence 
its use in gilding. 

Though the alloys of gold and the other metals 
already described are not put to any use, yet it is 
important to know, that many of these impair mate- 
rially its properties. Thus 9 o-Vo th part of lead sensi- 
bly affects it, and by merely exposing it to its vapour, 
its ductility is considerably diminished. When the 
lead amounts to about ^ th part, the alloy is as brit- 
tle as glass. 

Tin also impairs its properties. It is necessary, 
therefore, when it is to be alloyed with copper or 
silver, that these be quite pure, and particular atten- 
tion must be paid to this, with respect to silver, as 
the ores from which it is often procured contain lead. 

Gold is a very sparing production of nature. It 
is always found in its metallic state, either pure, or 
in combination with some other metal. In almost 
all civilized nations, gold is used as a medium of 
exchange. Jewellers' gold contains a considerable 
quantity of copper, or silver, or both, according to 
the colour required. 



272 ELEMENTS OF CHEMISTRY 

Gold is used also extensively in gilding other 
metals, and also wood, paper, and glass, for which 
purpose it is employed in leaf, in powder, and in 
amalgam. For procuring gold leaf, about two oz. 
are fused along with borax, and cast into an iron 
mould previously greased, after which it is heated, 
to burn off the tallow, and extended by beating, and 
by passing it between rollers, till it becomes as thin 
as paper. It is then cut into pieces of equal size, 
and again hammered till each becomes about an inch 
square, and about yy o th part of an inch in thickness. 
These are placed between pieces of vellum, and beat 
on a marble table, and after being extended, are again 
cut and hammered between pieces of ox gut, till they 
become of the requisite thinness, after which they 
are put up in books, the paper being covered with 
red bole, an impure sort of alum, to prevent them 
from adhering to it. In this operation, each grain 
affords about 30 inches of leaf, which is only about 
T8o!o oth of an inch in thickness. Gold powder is 
prepared by dissolving the metal in aqua regia, and 
putting into the solution a piece of copper, which 
unites with its oxygen and acid, and causes it to be 
deposited in its metallic state in fine powder, after 
which it is kept for some time in warm vinegar, 
washed, and dried by heat. Gold powder is also 
procured by heating its amalgam, by which the whole 
of the mercury is expelled, and by stirring it during 
the application of the heat, to prevent it from running 
together. It is then rubbed in a mortar with water, 
and dried. The mode of procuring the amalgam 
has been already described. 

The process of gilding differs according to the 
substance to be gilded. For gilding paper and wood, 
gold leaf is almost ahvays employed, the surface of 
the substance to be gijded being covered with some 
adhesive matter. That usually employed, is pre- 
pared by grinding together drj-ing oil and red ochre. 
That used by frame gilders, is merely strong size, to 



SILVER. 273 

which Paris plaster, or finely powdered chalk, has 
been added. With these the wood or paper is cov- 
ered, and the gold leaf applied, and gently pressed 
down with a flannel roller, the superfluous part being 
removed with a soft hair pencil. For gilding metals, 
the amalgam is almost always employed. When 
silver is to be gilded, after being washed with muri- 
atic acid, its surface is covered with the amalgam, 
and then by placing it on a charcoal fire, the mercury 
is driven oflf, and the gold left adhering to the silver. 
The loose particles are removed by a brush, and after 
covering it with gilder's wax, a composition of bees' 
wax, red ochre, verdigris, and green vitriol, it is 
heated and plunged while warm into cold urine, by 
which the colour is heightened. 

As copper is not easily acted on by gold amalgam, 
it is necessary to communicate to it a thin layer of 
mercury, which is done by immxcrsing it in a solu- 
tion of this metal in nitric acid, by which the mer- 
cury is deposited in its metallic state, and adheres 
to the copper. It is then gilded by means of the 
amalgam, the thin layer of mercury enabling it to 
retain the gold. Gilding of glass and porcelain is 
usually done by means of a flux, as borax. For this 
purpose the gold powder is mixed with ^um and 
borax, and applied by means of a pencil. The ware 
is then heated, by which the gum is burned off*, and 
the borax melted, causing the gold to adhere to it. 

For the method of procuring gold, see Silver. 

SILVER. 

Silver resembles gold in many of its properties, 
more particulary in its malleability, ductility, and 
power of resisting the action of acids. When 
pure, it is the whitest of metals, and is possessed of 
considerable lustre. It is harder and more elastic 
than gold, and next to it in malleability and ductility. 
It may be beat to leaves of only yg^oVo o^h part of an 
inch in thickness, and it can be drawn out to wire 



274 ELEMENTS OP CHEMISTRY. 

finer than a human hair, the tenacity of which is 
considerable. When of about y^^th of an inch, it will 
sustain a weight of 300 lbs. without breaking. 

When exposed to a w^hite heat it melts, but it is 
acted on by the air with very great difficulty ; even 
when kept in a state of fusion for a long time, it 
absorbs oxygen slowly. Very few of the acids act 
on it ; that commonly employed to dissolve it, is 
nitrous acid, with which it forms a compound, that is 
applied to useful purposes. For dissolving it, the 
acid must previously be diluted with about its own 
weight of distilled water, because common water con- 
tains impurities, which, acting on the silver, render 
the solution turbid ; and it is necessary, also, that 
the acid be quite pure, particularly free from muriatic, 
which common nitrous acid always contains. When 
the metal is put into the acid, it acquires oxygen 
from part of it, to form an oxide, which then enters 
into union with the remainder of the acid ; so that 
the salt is a nitrate. The solution is colourless, 
provided the metal is pure; but if sterling silver has 
been used, it is greenish, from the copper which it 
contains having been dissolved by the acid ; hence 
also the necessity of employing pure or virgin silver, 
when we require a pure nitrate. When the solution 
is evaporated to dryness, and the heat continued, the 
residue melts, and may then be poured into moulds. 
It is in this way that lunar caustic is prepared, 
w^hich is merely nitrate of silver melted, and poured 
into iron cylinders, previously greased. The solu- 
tion of the nitrate, when put on the skin, soon makes 
it black, and when rubbed on paper or cloth, it also 
very quickly undergoes a similar change ; hence its 
use as an indelible or marking ink. For preparing 
this, a piece of pure silver is put into its own weigjit 
of nitrous acid, diluted with an equal quantity of 
water ; and when the acid has taken up as much of 
it as it can, which is known by its ceasing to give 
oflf bubbles of gas, it must be poured off, and mixed 



DETONATING SILVER. 275 

with mucilage of gum arabic, which is to prevent it 
from running on the cloth, and also with a few drops of 
common writing ink to make it black, so that the traces 
made with it may be visible. When this is put on 
cloth, and exposed to light, the solution of silver 
becomes quite black, and is firmly fixed on the cloth; 
but, as the solution has frequently a slight excess of 
acid, to prevent the cloth from being acted on, it is 
necessary to wet it previously with a solution of 
an alkali, and dry it before putting on the ink. For 
this,- a tea spoonful of carbonate of ammonia, or 
smelling salts as it is commonly called, may be dis- 
solved in about 3 or 4 ounces of water. To prevent, 
as much as possible, any excess of acid in preparing 
the nitrate, there should be more silver employed 
than it can dissolve ; we ought to take care, therefore, 
that there be some left undissolved. 

Nitrate of silver is employed for afibrding a deto- 
nating compound. For preparing it, 50 grains of pow- 
der of lunar caustic are thrown, in small quantities at 
a time, into an ounce of a mixture composed of equal 
parts of nitric acid and spirit of wine, of specific 
gravity 860. An action commences, accompanied 
with the disengagement of red fumes, during which 
a white powder is deposited ; and when this has 
taken place, water must be poured on to put a stop 
to it. It may be also procured, by dissolving 30 
grains of pure silver in an ounce of diluted acid, 
(equal measures acid and water,) and adding, after 
the solution is completed, 2 ounces of alcohol. By 
the application of a very slight heat, the powder is 
deposited ; but the moment it appears, more spirit 
of wine must be put in, to prevent the action from 
becoming too violent. The powder thus formed, 
must be collected on a filter, and dried by exposure 
to air. When a little of the detonating silver is put 
into paper, and struck with a hammer, or when a 
little of it is rubbed in a mortar, it explodes with 
great violence. Hence its use in making detonat- 



276 ELEMENTS OP CHEMISTRY. 

i7ig balls 2inApiillaways. The former are prepared 
by wrapping up about |th of a grain, in a piece of 
very fine paper, with a dried pea. This, when 
thrown on the floor, is instantly exploded. The lat- 
ter are formed, by putting a little of the powder with 
sand between two pieces of thick paper, and securing 
these together, by pasting another piece of paper 
round that part containing the powder. When drawn 
asunder, the friction is sufficient to cause explosion. 

The solution of nitrate of silver is decomposed by 
some of the other metals; the most important action 
is with copper, as it affords a means of procuring the 
silver in a state of purity. If a plate of copper be 
put into the solution, it very soon becomes coated 
with silver; and on leaving it for some time, the 
former is dissolved, and the whole of the latter is 
deposited ; the copper having combined with the 
oxygen and acid of the other. The silver, when 
removed and washed, is quite pure. 

Silver unites with almost all the metals. The most 
important alloy is that with copper, iormmg Standard 
Silver. It is much harder than the pure metal, and is 
therefore better adapted for coins and trinkets. The 
Standard Silver of the U. S. consists of 1485 parts of 
fine Silver and 179 parts of copper. The dollar con- 
tains 416 grains of standard Silver, of which 371| 
grains are of pure silver, and 44| grains of alloy. 
The Troy pound of standard silver contains 10 ozs. 
14 dwts. 4/_ grains of fine silver, and 1 oz. 5 dwts. 
19y^3 grains of alloy ; and is coined into i3|| dollars ; 
or, 13 ounces of standard silver are coined into 15 
dollars.* Silver unites also with gold. It has been 
mentioned, that the latter is frequently alloyed with 
the former, for making jewellers^ gol<^« ^^ this 
alloy is more easily fused than sterlirjg gold, it is 
used for soldering it. 

Silver is used as a medium of exchange, and for 
trinkets and plate. It is employed also forgiving a 

* See Manual, p. 407. 



GOLD AND SILVER. ^77 

coating to other metals, with the view of making 
them appear like it ; or for enabling them to be put 
to purposes, to which they could not otherwise be 
applied. The only metals that are silvered, are cop- 
per, or brass, and pewter, the process differing 
according to the thickness of the coating required. 
An easy method of silvering is by the amalgam. For 
this, silver in powder, prepared from the nitrate by 
copper, as already described, is mixed with four 
limes its weight of common salt, four of sal ammo- 
niac, and a fourth part of corrosive sublimate, and 
made into a paste with water, with which the surface 
of the metal is covered, till the whole of it acquires 
a white metallic coating. This is an amalgam of the 
silver and the mercury of the sublimate, from which 
the latter is expelled by heating it, and the former 
is left adhering to the metal. Another mode of 
silvering is by lu7ia cornea. When muriatic acid, 
or a solution of sea salt, is added to nitrate of silver, 
a white powder is deposited, owing to the action of 
the muriatic acid on the silver. This is mixed with 
three of pearl ash, one of whiting and one of sea salt, 
and sprinkled on the metal previously melted, which 
gradually acquires a coating of silver; but as it is 
very thin, it requires to be varnished, to prevent it 
from being rubbed off. A more durable kind of 
silvering is given, by putting on a bar of copper, 
another of silver, of about -V^h part of the thickness, 
with a little powdered borax between them. By 
exposing this to heat, the borax is melted, and causes 
them to unite ; so that, by passing them between 
rollers, they can be extended to plates, the silver 
alvvays bearing the same proportion to the copper 
which it did at first. 

Methods of procuring Gold and Silver. 

Gold is always found in its metallic state, alloyed 
with silver and copper. Some iron and lead ores 
24 



218 ELEMENTS OP CHEMISTRY. 

also contain a sufficient quantity of it to make them 
valuable as ores of gold. When gold is alloyed with 
silver, mixed with stony matter, the method of ex- 
tracting it is very simple. The ore is first broken 
into pieces, which are arranged into heaps according 
to their richness. They are then freed as much as 
possible from stony matter, after which they are 
reduced to powder, and made into a paste with salt and 
water. Mercury is next squeezed through a leather 
bag on the mixture, and as it flows in, in very minute 
globules, it is mixed intimately with the ore. When 
the proper quantity is added, the whole is beat 
well together, and kept at about the temperature 
of boiling water for some days, by which the 
union of the mercury and gold is promoted. The 
earthy matter is then washed away, and the super- 
flous mercury is removed, by squeezing the mixture 
in a leather bag, after which it is placed in vessds, 
and subjected to distillation, by which the mercury 
is expelled, and the gold containing a little silver is 
left. These are easily separated by the process of 
parting. For this purpose the metal, being extend- 
ed to fine plates, is put into diluted nitrous acid, by 
which the silver is dissolved, and the gold is left, 
the former only being soluble in the acid. From the 
solution the silver can be precipitated, by the immer- 
sion of a piece of copper. 

In those cases in which the gold is alloyed with 
other metals, the process for procuring it is more 
complicated. The ore is first roasted, to drive off 
sulphur, and then heated along with lime and lead 
ore, and when completely fused, it is drawn off into 
moulds. The metallic matter thus obtained, after 
being repeatedly fused, is an alloy of gold, silver, 
lead, and copper, from the two last of which it is 
separated by the process of cupellation. Gold and 
silver are not oxidated by heat and air, while the 
others very quickly pass into the state of oxide when 
heated. On this depends the process of cupellation, 



CUPELLATION. 279 

which is merely the separation of gold and silver 
from other metals, by means of oxidation, which will 
be immediately described. 

Silver is obtained, not only from the ores of this 
metal, but also from those of lead ; some of which 
afford a sufficient quantity of silver, to make it of 
importance to extract this from them. Two modes 
are followed, amalgamalzo?i and fusion. The first 
is performed, by mixing the ore with sea salt, and 
heating it till the vapour ceases to come off". When 
the product is cool, it is reduced to powder, amalga- 
mated with mercury, and then heated, by which the 
mercury is driven off', and the silver is left, but still 
alloyed with copper. In conducting the process of 
fusion, the ore, which is generally one of lead, is 
roasted, to expel the sulphur, and is then heated 
along with charcoal, by which the lead is reduced, 
and melted, and falls to the bottom of the furnace 
carrying the silver with it. From the products thus 
obtained, the silver is procured by cupeliation. The 
vessel or cupel \n which the refining is carried on, is 
made of bone ashes. It is placed in a furnace, and 
when properly heated, the metal is put into it, and a 
stream of air allowed to pass over it, by which the 
oxidable metals are oxidated, and are absorbed by 
the dish, while the silver is left in its metallic state. 
If not pure, the process must be repeated. 

In freeing gold from other metals, recourse is often 
had to cupeliation, which is conducted in the same 
way as with silver ; but as the alloying metals are in 
small quantity, it is in general necessary to add some 
lead, which, during the process, is oxidated, and 
absorbed by the dish, carrying with it the whole of 
the impurities. Should ihe gold still contain sil- 
ver, they are separated by partings as already des- 
cribed. 

The process by which the value of gold and silver 
plate is ascertained, is conducted in the same way as 
that just described. Before a piece of plate can be 



280 ELEMENTS OF CHEMISTRY. 

stamped, it must be assayed, for which purpose, the 
assay-master scrapes oflF a little of it at different 
places, and subjects a certain weight of it to the pro- 
cess of cupellation, by which the baser metals are 
removed, and the gold or silver obtained. If the 
plate contain both of these, their proportion is ascer- 
tained by separating them after cupellation by nitrous 
acid, the weight of the undissolved metal giving 
the quantity of gold 5 the loss being the weight of 
the silver. 

PLATINUM. 

Platinuvi is found chiefly in South America, in 
small flat grains, but which are not the metal in its 
pure state ; they contain no less than four others, 
that have not been found any where else, and one or 
two more, which are very frequently met with. 
When pure, it is of a white colour, somewhat resem- 
bling silver, though rather darker, and having less 
lustre. In hardness it is inferior to few, if any, of 
the metals. It is possessed of great malleability and 
ductility. It may be beat into very fine leaves, and 
draw^n to wire, not exceeding ooVo^h part of an inch 
in thickness. When about the ^i^ih of an inch thick, 
it sustains a weight of 270 lbs. Platinum requires a 
higher heat than any other metal for its fusion, that 
of a blast furnace not being sufficient to melt it ; it 
may, however, be fused by the oxy-hydrogen blow- 
pipe. When heated to whiteness, like iron, it can 
be welded, and hence a method of getting it in its 
malleable state. It resembles gold in its power of 
resistiog the action of acids; the only one which 
dissolves it is nitro-muriatic, and for this purpose the 
best proportions are 3 of muriatic to 1 of nitric. 
When put into this, and heat is applied, it is slowly 
dissolved, but it requires the heat to be continued, 
otherwise the action ceases. The solution, which is 
of a brownish colour, like that of gold in the same 
acid, is a muriate. When muriate of ammonia is 



PLATINUM. 281 

added to it, it is decomposed, and a brown powder is 
deposited, which is a compound of the sal ammoniac 
and oxide of the metal, and which, when exposed to 
red heat, gives off the salt, while at the same time 
the oxide loses its oxygen, so that platinum in its 
metallic state is left, and hence the method of pre- 
paring spongy platinum^ for the hydrogen light- 
giving lamp, (^See page 151.) For this purpose, 
having dissolved it in aqua regia, a solution of sal 
ammoniac must be added, as long as there is any 
precipitation. The powder is then to be thrown on 
a filter, and after being washed and dried, must be 
exposed in a crucible to a red heat for a few minutes. 

Platinum combines with almost all the metals ; 
the alloys, however, are little known, and are not 
put to any particular use. When first introduced to 
Europe, its importation to Spain was prohibited by 
order of government, from an idea, that as it is of 
great weight, it might be used to adulterate^gold, — a 
prohibition which was unnecessary, for a little added 
to it impairs its properties so much, that it is easily 
detected. 

Platinum is obtained in different ways from the 
grains. One method is, by dissolving them in aqua 
regia, and decomposing the solution by sal ammo- 
niac, by which the spong}^ metal is procured ; and to 
get this in a malleable state, it is put into an iron 
mould, and compressed by means of a strong screw, 
--after which it is heated to redness, and repeatedly 
hammered, till it yields a uniform mass. It is also 
obtained in its malleable state, by mixing the sponge 
with mercury, and subjecting it to heat, by which 
the mercury is driven off. A number of pieces thus 
formed, are then put together, and welded. 

Platinum, from its infusibility, and its. power of 
resisting the action of chemical agents, is well adapt- 
ed for apparatus for chemists, though the difficulty 
of working it makes it very expensive. Hence its 

use as crucibles and evaporating dishes. On a larger 
24* 



282 ELEMENTS OP CHEMISTRY. 

scale, it is employed for making retorts in which 
sulphuric acid is boiled, after it is drawn off from 
the leaden chambers in which it is prepared. Instead 
of pure platinum, copper utensils coated with it are 
sometimes employed, by which the expense is con- 
siderably diminished. The coating is done in the 
same way as with silver, by covering the copper 
with an amalgam, prepared by mixing mercury with 
spongy platinum, and healing it, by which the former 
is driven off, and the latter left adhering to it. 

Platinum is also used in painting on porcelain. 
For this purpose, the sponge is mixed with a flux, 
and put on the ware, which is afterwards heated. 
In the same way, earthen ware vessels are often 
covered with platinum, by which they receive a 
resplendent coating, and thus become bad radiators, 
so that they are rendered better for retaining heat* 
/Seepage iOO.J 

MANGANESE. 

We are little acquainted with metallic manganese, 
as it is not used in this- state. The compound in 
general use in the arts, and for chemical purposes, is 
that sold under the name of manganese, which is 
an oxide. It is a black earthy looking body, found 
principally in Aberdeenshire and Cornwall. It is 
brittle, and when recently broken, has considerable 
lustre. When exposed to a strong heat, it is decom- 
posed, and part of its oxygen is given off. Hence a 
method of procuring this gas, indeed it is the one 
generally resorted to, when required in large quantity. 
For this purpose, the oxide reduced to coarse powder, 
is put into an iron bottle, a, to which /T^^^^:^^^::^::-. 
a tube, b, is adapted. By putting the /fJS. S 
bottle in a fire, so as to bring it to a 
red heat, a little watery vapour is at a 
first given off, after which oxygen gas 
is disengaged. By connecting a gas- 



holder with the tube, 6, it is very quickly filled. In 



MANGANESE. 283 

this instance, there remains in the bottle a brownish 
powder, which is manganese, still in union with 
oxygen, so that the whole of the oxygen has not 
been given off, nor can it be expelled in this way, 
even though the heat be continued. 

The acids act easily on oxide of manganese, but 
the products differ according to the acid employed. 
When sulphuric acid is poured on it, and heat is 
applied, oxygen gas is disengaged. Hence another 
method of preparing this elastic fluid. For this pur- 
pose, the oxide reduced to pow^der is put into a retort, 
and on it an equal weight of sulphuric acid is poured. 
By applying heat, a gas comes off, and may be col- 
lected in the jars on the water trough. Before begin- 
ning, however, to collect it, it is necessary to try 
when it is coming off pure, which is done by filling 
occasionally a small phial with it, and putting into it 
a piece of wood recently extinguished, but w^hich is 
still red. When it is rekindled, the oxygen is suffi- 
ciently pure, and may then be collected. Here, as in 
the former experiment, part only of the oxygen gas 
is driven off from the oxide, the remainder being left 
in union with the metal, w^ith w^hich the sulphuric 
acid has united. 

The action between the oxide and muriatic acid is 
also important, as affording a means of procuring 
chlorine gas. For this purpose, the oxide in powder 
is mixed in a retort with four parts of acid, and a 
very slight heat is applied, by which the gas is ex- 
pelled, and may be collected in jars, or boitles, on a 
trough, the water of which must be warm (to about 
70^ or S0°) to prevent the gas from being absorbed. 
If the gas is to be kept, it must not be left over 
w^ater ; it is better, therefore, to collect it in bottles, 
the stoppers of which can be secured by luting. 
Muriatic acid being a compound of chlorine and 
hydrogen, when poured on the oxide of manganese, 
and heat applied, the hydrogen of part of the acid 
unites with the oxygen of the oxide, to form water, 



284 ELEMENTS OF CHEMISTRY. 

the chlorine, the other ingredient of the acid, is 
disengaged. The remainder of the muriatic acid 
not decomposed, combines with the manganese, 
still retaining part of the oxygen to form a muriate. 
When chlorine is prepared on a large scale, instead 
of muriatic acid, a mixture of sulphuric acid and sea 
salt is used, by which the previous preparation of 
the muriatic acid is avoided ; because the sulphuric 
acid acting on the salt, unites with its alkali, and dis- 
engages its muriatic acid, v^hich then acts on the 
oxide in the same way as when muriatic acid alone 
is employed. Hence the method of preparing the 
gas, in making the bleaching compound, the oxide, 
oil of vitriol, and salt, being mixed in a retort, and 
heated, by which the gas comes off, and is passed 
through slaked lime. {See page 221.) 

Besides the uses to which oxide of manganese is 
applied, as already mentioned, it is employed in 
glass-making, for destroying the colour communicat- 
ed by impurities, principally iron. {See page 230.) 
By the addition of a certain quantity of oxide to 
glass, it becomes of a rich purple colour, and hence 
its use in imitating some of the gems. 

BISMUTH. 

Bismuth^ when pure, is white, with a slight tinge 
of red. It is not possessed of much malleability, nor 
ductility, nor has it much tenacity, a wire of Vth 
of an inch in thickness, sustaining a weight of only 
30 lbs. without breaking. Its melting point is very 
low, becoming fluid at about 460. It is easily acted 
on by acids, but the compounds formed present noth- 
ing interesting. 

Bismuth is employed chiefly in its metallic state, 
particularly for communicating fusibility to other 
metals, as in forming solders, a little of it being 
sometimes mixed with the tin and lead employed 
for this purpose, and it is used also in making some 
kinds of pewter. When it is mixed in large quan- 



COBALT. 285 

tity with tin and lead, the alloy is so fusible, that it 
is melted when thrown into boiling water ; and if to 
this a little mercury be added, the fusing point is 
still farther reduced ; hence the use of these mate- 
rials in m^k.mg fusible inetah This is prepared by 
fusins: together 9 of bismuth, 5 of lead, and 3 of tin, 
and then adding 2 of mercury. The fusing point of 
this alloy is about 150°. Hence an amusing experi- 
ment with it is to have a table spoon or tea spoon 
made of it, and give it to a person to take his soup 
or tea, the temperature of which causes the spoon 
to be melted. 

Bismuth is occasionally found in its metallic state, 
but it generally occurs in union with oxygen or sul- 
phur, from which it is ahwa} s obtained. For this 
purpose, the ore is first roasted, generally along with 
fuel, in shallow pits dug in the earth. The metallic, 
matter collected at the bottom is then put into a cru- 
cible, with charcoal, and covered wn'th sea salt : heat 
is applied for a short time, by which the mixture is 
fused, and the bismuth falls to the bottom, the char- 
coal having deprived it of its oxygen, and allowed it 
to assume the metallic state. It is not, however, 
pure, it contains a little lead, and sometimes silver; 
but it is sufHeiently so for the purpose to which it is 
usually applied. 

COBALT. 

A mineral called cobalt^ has been long in use for 
giving a blue colour to glass, which has been found 
to contain a peculiar metal, possessed of remarkable 
properties, though not much used in the arts. When 
pure, it is of a bluish colour, is soft and brittle, so 
that it is easily reduced to powder ; it is seldom, 
however, prepared in its metallic state, unless for 
chemical purposes. When used in the arts, it is in the 
form of an oxide, of which there are two kinds, zaffre 
and smalt. To prepare zaffre, cobalt ore, which, 
besides cobalt, contains arsenic and other impurities, 



286 ELEMENTS OP CHEMISTRY. 

is exposed to heat, during which a considerable quan- 
tity of vapour is given off, which is conveyed through 
flues into reservoirs, where it is condensed. When 
these have ceased, it is removed, powdered, and a 
second time heated, after which it is again reduced 
to powder, and mixed with that of flints. Smalt is 
procured by roasting zaffre with potassa for about 12 
hours, and pouring it, when fluid, into water, by 
which it is afterwards more easily reduced to powder. 
It may also be obtained, by exposing to a strong 
heat, a mixture of cobalt ore, flints, and potassa, by 
which the previous preparation of zaffre is avoided. 
When properly formed, it is a blue glassy looking 
substance, hence sometimes called azu7'e blue. It 
is used for giving colour to glass and porcelain. 
When mixed in very small quantity with the former, 
it makes it of a deep blue, 2 or 3 grains being suffi- 
cient to colour half an ounce. It has the advantage 
of not being destroyed by heat, a property not pos- 
sessed by other substances used for the same purpose. 
Smalt, when mixed with starch, forms blue used 
in washing linen, to prevent it becoming yellow. 
Zaffre is employed also for affording a very fine sym- 
pathetic ink, that is, a substance which will change 
its colour by heat or moisture. For this purpose, it 
is thrown in small successive portions into muriatic 
acid, previously mixed with about its own weight of 
water, and heated, and the action continued till the 
acid will not dissolve any more, after which it is 
boiled, to expel the superabundant acid, and filtered. 
W^hen used as a sympathetic ink, it must be diluted 
w^ith water, till it becomes colourless. Traces drawn 
with it on paper are invisible, but when slightly 
heated, become of a fine blue colour. As the paper 
cools, the traces disappear, and the more moist the 
atmosphere, the more rapid is the change, so that 
it is owing entirely to the state of the paper with 
respect to moisture. They may be again restored, 
merely by heat;, and these changes may be effected 



ARSENIC. 287 

any number of times, provided care is taken not to 
injure the texture of the paper. If the solution 
of cobalt be mixed with other substances, different 
colours may be imparted. Thus, if a little gamboge 
be added, the solution gives yellow traces, but which, 
when dried, become green, this being produced by 
the yellow of the gamboge and blue of the cobalt. If 
mixed with lake, they become purplish when heated, 
the red and blue yielding purple. Amusing experi- 
ments may therefore be performed with these solu- 
tions. Thus, when we wish to make a landscape 
change its appearance, say from a winter to a summer 
scene, the trunks of the trees are coloured brownish, 
while the leaves and fore ground are covered with 
the cobalt solution, to which a very little gamboge 
is added, but not so much as to give it colour. On 
heating the paper, the leaves and fore ground become 
green, and thus change the landscape from winter to 
summer. 

ARSENIC. 

When describing the method of procuring zaffre, 
it was mentioned, that vapour is given off from the 
cobalt ore, which is conveyed by flues into reser- 
voirs, in which it is condensed. This is white 
arsenic^ or as it is generally called arsenic, but im- 
properly so, because it is not arsenic in a state of 
purity, but a compound of it and oxygen. Arsenic 
is not employed in the arts in its metallic state ; the 
compounds in general use are white arsenic, which, 
as has been said, contains oxygen, and realgar and 
orpiment^ which are sulphurets, or compounds of 
arsenic and sulphur. 

White arsenic is generally prepared by subliming 
the condensed vapours given off from many of the 
ores in preparing the metals, but particularly from 
those of tin and cobalt. For this purpose, large cast 
iron boxes, having conical tops, are brought to a red 
heat, and the ore, reduced to fragments, is thrown 



23S ELEMENTS OF CHEMISTRY. 

in, and the lid instantly put on. When the whole 
of the volatile matter has sublimed, more of the ore 
is introduced, the lid being shut dovvn the moment 
it is put in ; and in this way the process is con- 
tinued till a considerable quantity of white arsenic is 
sublimed, and condensed in the cover. It is then 
removed, and freed from any impurities adhering to 
it. As thus procured, it is in large white cakes, 
which are very compact, but easily reduced to 
pow^der. It has a disagreeable taste, and is one 
of the most virulent poisons with which we are 
acquainted. 

When heated, it is very quickly volatilized, as may 
be shewn by throwing it on a hot plate of iron, or 
by holding a little of it on the point of a knife, over 
the flame of a candle. When mixed with charcoal, 
and heated, it is decomposed ; the charcoal combines 
with its oxygen, and flies ofl'in the form of carbonic 
acid gas, while the arsenic is reduced to its metallic 
state ; and hence a method of obtaining metallic arse- 
nic. This is easily shewn on a small scale, by put- 
ting the mixture into a glass tube, so as to occupy 
about an inch at the bottom, and holding it over the 
flame of a candle ; metallic arsenic soon rises in 
vapour, and adheres to the cold part of the tube, 
giving it a bright coating like that of a mirror. 

Orpiment and realgar are both natural productions, 
but they are also prepared artificially. The former 
is procured in the same way as white arsenic, with 
this difference, that a little sulphur is mixed with the 
ore, before it is put into the iron box. On the appli- 
cation of heat, a substance is sublimed, which, when 
condensed in the cold cover, is of a yellowish colour. 
When this is fused, it becomes brown, forming real- 
gar. 

White arsenic is employed in glass-making for 
various purposes ; but as it is very volatile, it is 
necessary to add a little nitre, the potassa of which 
unites with it, and prevents it from subliming at the 



ANTIMONY. 289 

heat to which it is exposed. When employed in 
proper quantity, it makes the glass more transparent; 
but if too much be used, it renders it whitish, and 
this is increased by age. 

Orpiment and realgar are used by painters for 
making yellow and red paints. 

ANTIMONY. 

The substance sold under the name oi antimony^ 
is of a dark blue colour, and metallic lustre. It was 
formerly supposed to be a metal, but it is now known 
to contain sulphur, in union vvith a metal called 
antimony ; it is therefore a sulphuret. It is a natu- 
ral production, but before being used, it is always 
purified. For this purpose, the ore is put into large 
crucibles, from the bottom of which there proceeds 
a tube, that terminates in a receiver. The crucibles 
being placed in a furnace, heat is applied, by which 
the sulphuret is melted, and escapes into the receiver, 
where it is congealed. In this state it is sold under 
the name of antimony ^ crude antimony ^ and black 
antim^ony ^ and from which the metal is obtained in 
the usual way, first by roasting it exposed to the air, 
by which the sulphur is expelled, and the metal 
acquires oxygen. After this it is reduced to powder, 
mixed with charcoal, and again heated in crucibles, 
in the bottom of which the metal gradually collects. 

Antimony is not itself put to any particular use. 
It is only when in alloy, or in the state of oxide, 
that it is employed in the arts. 

When equal parts of metallic antimony and lead 
are melted, the product, when cold-, is porous and 
brittle ; but as the portion of the latter is increased, 
the brittleness is diminished. When I of antimony 
and about 4 or 5 of lead are fused, they form type 
metal J which is harder than lead, and possesses the 
valuable property of expanding during its congela- 
tion ; hence it takes an excellent impression, when 
25 



290 ELEMENTS OF CHEMISTRY. 

thrown fluid into a mould. Owing to this, it is also 
occasionally used for taking casts from medals. An- 
timony combines also with tin, and forms one sort of 
pewter. The name oi pewter is given to any white 
malleable alloy, containing a considerable quantity of 
tin ; but its composition varies in different places. 
The finest kind is composed of about 100 parts of tin, 
8 of antimony, 4 of copper, and 1 of bismuth, the 
use of which is to render the tin harder, and enable 
it to retain its lustre. The alloy of tin and antimony 
forms also the metal on which music is engraven. 

Antimony, in union with oxygen, is used for giv- 
ing a yellow colour to earthen-ware, and in forming 
glass of the same colour, as in imitating some of the 
gems. The oxide employed by potters, is prepared 
by burning a mixture of equal weights of crude anti- 
mony and nitre. For this purpose, it is thrown into 
a red hot crucible, in small quantities at a time. It 
burns wdth a bright flame, and a substance of a dark 
brown colour is left in the vessel, which, after being 
reduced to powder, is well washed with warm water, 
to remove impurities. In this process the sulphur is 
driven off*, and the antimony acquires oxygen from 
the nitre. A substance of a similar nature is prepar- 
ed, merely by roasting crude antimony exposed to 
the air, and afterwards increasing the heat, to fuse 
the product. When cold, it is a brown glassy look- 
ing matter, and hence called glass of antimony. 

The oxides thus procured are not pure. A much 
finer sort is prepared, by dissolving crude antimony 
in muriatic acid, by the application of a slight heat. 
For this purpose the acid, put into a flask, is heated, 
and the ore, reduced to powder, is thrown in, in 
small successive portions ; when the acid is saturat- 
ed, the solution is filtered, and poured into water, 
b}'- which a white powder is thrown down, w^hich 
must be collected on a filter, washed, and dried by 
heat. In this process, tlie water takes away the 
acid from the solution, and the oxide is precipitated. 



VINOUS FERMENTATION. 291 

This is much purer than the others, and gives a finer 
yellow to glass and earthen ware. 



VEGETABLES. 

All vegetables have a determinate form, and their 
internal structure is very delicate ; but these vary in 
almost every distinct class. Notwithstanding this 
great diversity, they do not contain many chemical 
elements ; indeed, with the exception of a few, they 
have only oxygen^ hydrogen^ and carbon^ and with 
these there is a little earthy and metallic matter, the 
nature of which varies according to the soil in which 
the plant has been raised. 

When vegetable matter, wood for instance, is 
exposed to a strong heat, excluded from the air, a 
watery fluid is given off, containing the acid of vin- 
egar, and along w^ith it, carburetted hydrogen is 
disengaged. After these have ceased to come off, a 
substance is left in the vessel, still retaining the form 
£>f the wood, and which is charcoal. 

When the vegetable is heated in air, it burns, and 
carbonic acid and water are the products, and it is 
consumed, leaving only a minute quantity of ashes. 

Vegetables also undergo changes, by which their 
nature is completely altered, and new substances are 
formed. This process is called fermentaiion^ and 
is divided into three kinds, the vinous^ acetous^ and 
putrefactive ; the first so called, because, during it, 
vinous or spirituous fluid is formed, the second, 
because vinegar or acetic acid is produced, and the 
third, because the vegetable undergoes putrefaction. 

VINOUS FERMENTATION. 

Sugar is the substance that assumes the spirituous 
fermentation most easily, and by converting other 
bodies to the saccharine state, it causes them to 



292 ELEMENTS OF CHEMISTRY. 

undergo the change more readily. When sugar is 
dissolved in water, and a little yeast is added, the 
mixture soon becomes muddy, bubbles of gas rise 
through it, and it acquires a thick scum on its sur- 
face. When these changes have taken place, the 
scum falls to the bottom, and the fluid again becomes 
transparent ; its properties are also altered ; it has 
lost its sweetness, and acquired a hot pungent taste, 
and produces intoxication. 

When vinous fluids are exposed to the air, they 
become turbid ; their temperature rises and a scum 
collects on the surface. After these changes cease, 
4he fluid again becomes transparent, and loses its 
grateful flavour, and intoxicating quality, and acquires 
a sour taste. In this case the product is vinegar, 
which contains as one of its ingredients, an acid called 
acetic acid. When the product of this fermentation 
is exposed to the atmosphere, the putrefactive pro- 
cess commences ; it becomes opake, acquires a disa- 
greeable smell, and in the course of time, almost the 
whole of it is consumed, leaving only a little carbon 
and earthy matter. 

There are different circumstances necessary to 
cause the commencement, and favour the progress 
of vinous fermentation ; such as, a certain quantity of 
water, a proper temperature, and in general, the 
addition of a body called di ferment. The tempera- 
ture ought to be from 50 to 80; when below the 
former, it goes on slowly ; the nearer it is to the lat- 
ter the better, but it must not be allowed to go beyond 
it, as the acetous fermentation is apt to begin. The 
substance added to induce fermentation is yeast, 
which is the scum and sediment collected from liquids 
in which fermentation is going on. 

By vinous fermentation, are produced the dif- 
ferent liquors which are possessed of intoxicating 
quality ; they may be divided into two kinds, the 
vinous, obtained from the juices of plants, and the 
different kinds of beer ^ procured from the infusion of 
seeds. 



BREWING. 293 

The process of making wine is very simple. From 
grapes there is expressed a juice called 'must, which 
contains sugar, jelly, and cream of tartar. When 
kept at about the temperature of 70, fermentation 
commences, and goes on with the usual occurrences ; 
and after it has ceased, the liquor is put into casks, 
where it slowly deposits the substance called tartar j 
which is composed chiefly of cream of tartar and the 
colouring matter of the wine, and from which cream 
of tartar is obtained, merely by dissolving it in 
water, filtering, and boiling down, by which the salt 
is separated, and as it rises to the surface during the 
ebullition, it is skimmed off; hence its name cream 
of tartar. 

The colour of wine is communicated by the husks, 
which are mixed with the fermenting fluid, and the 
sparkling wines, as champaign, derive this property 
from their containing a large quantity of carbonic 
acid, generated during the fermentation, the wine 
being bottled before this process is finished. 

Malt liquors, as the other kinds of fermented 
fluids are called, are obtained from grain, for which 
purpose barley is used ; but before inducing fermen- 
tation in it, it is previously converted into malt. 
For this purpose, it is put into a large trough, and 
mixed with as much water as merely covers it, where 
it remains for two or three days, the time depending 
on the weather ; the warmer the season, the less 
being required. Here it imbibes moisture, emits 
carbonic acid, and the water dissolves a little of it, 
particularly of the husk. This process is called steep- 
ing. When completed, the grain is spread on the 
malt floor to about the depth of 16 inches, where it 
begins to grow warm, and it emits a pleasant odour^ 
resembling that of apples ; it also becomes moister 
than before ; hence this stage of the process is called 
sweating. When these changes have taken place,, 
the roots of the grain shoot forth, and in the course 
of another day, the future stem called acrospire^ 



294 ELEMENTS OF CHEMISTliy. 

begins to appear. To put a stop to the farther pro- 
gress of the changes that are going on, the depth of 
the grain is gradually diminished, till at last it is only 
about 3 inches deep, after which it is put into a kiln 
and subjected to heat, at first slight, but afterwards 
gradually increased, till it is sufficiently dried. By 
this last part of the process, the germination or 
growth of the seed is stopped, the malt is then put 
into wire sieves and shaken, by which the roots, or 
comings as they are called, which were formed 
during the first stage, are removed. 

Having procured malt, the next operation is to 
subject it to brewing, w^hich consists of five parts, 
Tnashing, boiling, cooling, fermenting, and cleans- 
ing. The malt, after being bruised, by passing it 
between large iron rollers, is put into a mash tun 
with about an equal quantity of water at 180^, and 
well stirred. After remaining there for a few hours, 
the fluid is drawn ofi", and the process repeated, till 
the whole of the soluble matter is extracted. The 
product called wort, is a dark brow^n liquid, having 
a sweet taste, which it has acquired from the saccha- 
rine matter of the malt. It is pumped off into boil- 
ers, in w^hich it is boiled for some hours, till it becomes 
of the requisite strength, and which is known by the 
use of an instrument called a saccharometer, which 
indicates not only the specific gravity, but also the 
quantity of soluble matter in each barrel of wort; and 
it is by this that the duty is levied, brewers paying 
according to the strength of the wort. It is while 
undergoing the pi^ocess of boiling, that the substan- 
ces are added which communicate the proper flavour. 
That usually employed is hops, the seed pods of a 
plant much cultivated in England, particularly in 
Kent and Hampshire. These contain an oily matter, 
and a hitler substance, both of which are extracted 
by the wort, and impart their qualities to it. The 
quantity of hops employed v^sries in different places ; 
in general about one lb. is used for each bushel of malt 



BREWING. 295 

but this depends entirely on the required strength of 
the fluid. When the wort is properly boiled, it is 
drawn off into the coolers, large shallow troughs 
placed in apartments in which there is a free ventila- 
tion, by having the sides made of frame work. Into 
these it is poured to about the depth of three or four 
inches, so that it may become cool as quickly as pos- 
sible, and thus be prevented from becoming sour. 
When cooled, it is run off into the fermenting vats 
ox gyle tuns ^ in which it is to undergo fermentation. 
It is then mixed with the requisite quantity of yeast, 
by which the fermentation is induced ; bubbles of 
gas come off, and a scum rises to the surface, the 
temperature at the same time increases, in general, 
from about 12 to 15 degrees. After it has gone on 
for a few days, it becomes languid, the wort and the 
froth collected on its surface are then well mixed, 
by which it again commences, and continues for 
some time ; at last the fluid diminishes in the vat, 
owing to the air bubbles escaping from the froth. 
When it has arrived at this state, it is necessary to 
stop the fermentation, otherwise the scum would mix 
with the fluid, and not only give it a bitter taste, but 
cause it to become sour. It is therefore drawn off 
into barrels, which are filled quite up to the bung 
hole. In these the fermentation again begins, by 
which a scum rises to the surface ; and as the barrels 
are always kept full, by occasionally pouring in a 
little of the liquor, it ivorks over^ the scum is there- 
fore thrown out, and thus prevented from mixing 
with the fluid, at the same time part of the yeast 
fails to the bottom, forming the dregs ; hence this 
part of the process is called fining or cleansing. 
When the fermentation has stopped, which is known 
by the froth ceasing to vv^ork over, the barrels are 
bjn2;ed, and are ready for the market. 

The process now described, is that followed in 
making ale and beer ; the brewing ^ «* porter is car- 
ried on in the same way, with this difference, how- 



^96 ELEMENTS OF CHEMISTRY. 

ever, that the malt is prepared in a peculiar way. 
It has heen already said, that that used for ale is 
dried by the application of a slight heat. In making 
malt for porter, a much hio;her temperature is ap- 
plied, by which it is slightly burned, so that the 
wort got from it has a dark colour, and a peculiar 
bitter taste. 

All vinous and malt liquors contain a quantity of 
spirit of wine, or alcohol, formed during the fer- 
mentation, which is the cause of their intoxicating 
quality, and which can be procured from them mere- 
ly by distillation. Hence the mode of making whis- 
ky, rum, gin, brandy, and other spirituous fluids. 

The substance generally employed in making 
lohisky^ is barley, but occasionally, sugar, molasses, 
carrots, turnips, &c. are used. When grain is 
used, it is previously malted, as has been already 
described. Distillation, as the making of whisky 
is called, consists of four parts, mashing, coolings 
fermenting, and distilling, the three first of which 
are carried on nearly in the same way as in brewing ; 
the wort being obtained by mashing the malt, and 
then cooling it as quickly as possible, and after mix- 
ing it with the requisite quantity of yeast, making it 
undergo fermentation, by which the sugar it contains 
is gradually decomposed, and converted into alcohol, 
or spirit of wine, by which the specific gravity of 
the fluid is diminished ; it is therefore said to be 
attenuated. Spirit of wine has the power of stop- 
ping fermentation ; when, therefore, it is generated 
in too great quantity in the fermenting tun in pro- 
portion to the water, it prevents in a great measure 
the process from going on, consequently part of 
the sugar is not decomposed and converted to 
spirit 5 it is of importance therefore to keep the fluid 
weak. 

The liquid thus procured is called wash, and is 
subjected to distillation as soon as the fermentation 
has ceased; otherwise it becomes sour. The appara- 



PISTILLATION. 



297 




tus employed, con- 
sists of a copper 
still, a, to the up- 
per part of which 
is fixed a tube that 
is bent downwards 
and then makes 
several turns 6, in a 
reservoir of water, 
c ; it is therefore 
called a loorm^ and the reservoir is termed a refrig^ 
eratory ; and to keep this as cool as possible, that it 
niay quickly condense the vapour, a stream of water 
is made to pass through it. Having put the wash 
into the still, and fixed on the tube, a strong fire is 
kindled beneath it, and when the liquor is properly 
heated, the spirit rises in vapour, being more vola- 
tile than the water, and as it flows through the worm 
is condensed, and passes out at the opposite end, d^ 
where it is collected in receivers. The distillation 
is continued, till the fluid which comes from the 
worm is of the specific gravity of water, and which 
is known by the use of an areometer^ what is 
still left in the still is called spent luash^ and is 
used for feeding cattle. The liquid obtained by 
the first distillation is called low wines ; it contains 
about a fifth part of its weight of alcohol. It is sub- 
jected to a second distillation or doubling, and the 
process continued till the fluid is got of the requisite 
strength, which, in Great Britain, is by order of 
government 909, water being 1000. 

The mode of carrying on distillation has varied at 
different times, according to the manner of levying 
the duty. Distillers formerly paid according to 
time. It was calculated how much spirit could be 
obtained in a given time, from a still of a certain size, 
and when a distiller began his operations, all that 
was necessary was to find the dimensions of the still, 
and the duty was levied according to the time it was 



298 ELEMENTS OP CHEMISTRY. 

in operation. This induced distillers to make altera- 
tions in their stills, by which the distillatioti was 
carried on more rapidly than was calculated. The 
act of parliament allowed 8 minutes for a still of SO 
gallons, but by making the still very broad, and hav- 
ing a brisk fire under it, the process could be com- 
pleted in much less time. In some distilleries, a 
still of 80 gallons could be charged, run off, and 
ready for another charge in about 3 minutes, so that 
the distiller was getting double the quantity of spirit 
that he paid duty for. In carrying on distillation in 
this w^ay, it was necessary to put a piece of soap into 
the still, the oily matter in which rose, and spread 
over the surface of the wash, and by breaking the 
large bubbles, prevented it from coming over, or 
running foul ; and hence the disagreeable soapy 
taste that whisky had ; besides, it contained more of 
a peculiar essential oil, derived from the malt. Dis- 
tillers now pay duty according to the strength of 
their wash, and the quantity of spirit, taking care 
that the latter is of the proper strength ; hence it is 
that whisky is now far superior to w^hat it formerly 
was, the spirit being distilled off more gradually, and 
bringing with it less of the substances that gave it 
the disagreeable flavour. 

Before finishing this subject, it is necessary to 
explain a term much used when speaking of whisky. 
By order of government, Vv^hisky must be of a cer- 
tain strength, and is then {i2\\^^ proof sjnr it. It is 
often said, however, to be 5 or 10 above proof, by 
which is meant, that 100 gallons of the former will 
require 5, and of the latter 10 of water, to make 
them proof 

Gin^ or Hollands^ is ahvays prepared by the 
Dutch. The wash employed is procured by ferment- 
ing a mixture of malt and rye^ and after the fermen- 
tation is completed, it is put into the still along with 
juniper berries, and the distillation carried on in the 
usual way, by which a spirit is obtained having the 
peculiar flavour; derived from the junipers. 



ALCOHOL. ' 299 

Rum is procured by subjecting to distillation, a 
fermented fluid prepared from the refuse in the ope- 
ration for making sugar; the peculiar flavour being 
derived from an essential oil existing in the juice of 
the cane, and which is brought ofi' by the spirit. 
The fluid procured by the distillation, which is re- 
peated till it is of the proper strength, is colourless, 
and is coloured by the addition of a little burnt 
sugar. 

Brandy is obtained merely by distilling wine, of 
course its strength and flavour must depend on those 
of the wine. The distillation is performed in the 
usual way, by which a colourless spirit is procured, 
which is afterwards coloured, by mixing with it 
some burnt sugar, and a dye called Saunders wood. 

From all of these substances, alcohol, or spirit of 
wine, may be prepared. Whisky is employed in 
this country, and brandy on the continent. All that 
is requisite is to put the spirituous fluid into a still, 
«, {See page 297), and subject it to distillation, till 
about one half comes over, the vapour, as it passes 
through the refrigeratory, 6, being condensed, may 
be collected in the receiver at d. As thus procur- 
ed, it is not pure; it still retains a good deal of water, 
and an essential oil, from which it may be in a great 
measure freed by frequent distillation from potassa. 
For this purpose, the potassa is exposed to a red 
heat, and when cooled to about 300, is mixed with 
the spirit of wine. After leaving them together 
for some time, the clear then to be poured off, 
and the process repeated two or three times, after 
which the liquid must be again subjected to distilla- 
tion, reserving only the first parts that come over, 
provided it is required very strong. 

ALCOHOL. 

Alcohol, as thus procured, is a transparent colour- 
less fluid, possessing strongly intoxicating qualiiies. 
Its specific gravity of course varies according to the 




300 ELEMENTS OF CHEMISTRT. 

method by which it is prepared. That from the 
first distillation of whisky is about 860, water being 
1000; but by repeated mixture with potassa, and 
distillation, it may be easily got of 817. When ex- 
posed to heat, it takes fire, and burns without smoke, 
owing to which it is frequentl}^ employed for heat- 
ing small vessels, for which purpose it is always 
consumed on a cotton wick. The lamps 
are made either of brass or glass, and ought 
to have a cap, fir, to fit on the neck, 6, 
over the wick to prevent the waste of the 
alcohol when not required. 

The action between alcohol and some of the 
metals, particularly platinum, is remarkable. When 
a small piece of thin platinum leaf, suspended 
by a wire, is heated by a spirit lamp, and then 
quickly put into a glass, in which there is 
a little alcohol, so as to have it just over 
the surface, and of course in the vapour 
arising from it, it continues red hot, as long 
as there is any fluid in the jar, which is owing to 
the vapour undergoing a sort of combustion, and 
generating heat sufficient to keep the metal in that 
state. Hence the lamp without flame, which 
merely a common spirit lamp, but having a 
spiral of platinum wire, about the thickness 
of the jV^^^ P^^^ ^f ^^ inch, placed round 
the wick, but not in contact with it. On 
kindling the spirit, the platinum becomes 
red hot, and on extinguishing the flame, the vapour 
coming off, keeps it ignited, so that, on applying a 
match, it kindles it, which also sets the spirit on 
fire. 

Jlcetous Ferment aiio7i. 

Every substance that undergoes the vinous, passes 
into the acetous fermentation. There are besides 
many bodies which at once run into the latter, as is 
particularly the case with those that contain a great 





ACETOUS FERMENTATION. 301 

deal of mucilaginous matter, and little sugar. Alco- 
hol, when pure, does not undergo acetous fermenta- 
tion, but if it contain vegetable matter, a change 
takes place in it; hence the reason why wines 
become sour, and why weak ones do so sooner than 
strong ones, the former having little alcohol, and a 
good deal of vegetable matter, while the latter have 
much alcohol, and little vegetable substance. Wine 
w^hich has been deprived of its vegetable matter by 
clarification does not become sour, but if some of this 
be put in, acetous fermentation commences under 
favourable circumstances. Certain things are neces- 
sary for this change taking place. The fluid must 
be kept at a particular temperature, between 60 and 
80 is the best, but if it fall below 50, the fermenta- 
tion stops. It must also be exposed to the air, other- 
wise it does not take place ; hence the reason why 
spirituous and malt liquors do not become sour, when 
kept in -well corked bot ties. The presence of some 
substance that acts as a ferment is also necessary, 
which may be either the sediment from a fluid that 
has undergone the process, or some yeast. It appears 
that sugar is the, essential ingredient in those fluids 
that undergo acetous fermentation, and the quantity 
of vinegar formed is to a certain degree in proportion 
to the sugar y thus, 7 of water and 1 of sugar, with a 
little yeast, form vinegar ; if more sugar be used, 
part of it is left undecomposed. In those countries 
where grapes abound, vinegar is generally prep:)red 
from wine. In England it is usually obtained from 
grain. That from wine is reckoned not only the 
best, but least liable to decay, for, when prepared 
from grain, it contains vegetable matter, which causes 
it to become mouldy ; but this may in a great meas- 
ure be prevented by boiling, by which the vegetable 
matter is coagulated, and maj be removed. 

In manufaciuring vinegar from malt, a wori is 
made in the usual way, by washing it with water, 
and mixing it with yeast, which is put into barrels^ 
26 



302 ELEMENTS OF CHEMISTRY. 

and kept at a moderate heat for some weeks, during 
which it becomes sour, having previously passed 
through the vinous stage, and afterwards run into the 
second or acetous. Vinegar is often made on a small 
scale, for which purpose sugar is dissolved in water, 
or fruit, as currants or gooseberries, are mixed with 
water, and to these there is added a little yeast. The 
whole is put into a cask, which is kept in a warm 
room till it is known by the taste to have become 
sufficiently sour, after which it is bottled and corked, 
to prevent it from becoming mouldy. 

Vinegar is now manufactured on a large scale by 
subjecting wood to distillation, a process much prac- 
tised for preparing that employed in the arts, as in 
the preparation of the different salts containing it. 
For this purpose, wood is put into large cast iron cyl- 
inders, and heated to redness, by which its elements 
are made to enter into a new state of union, and gen- 
erate vinegar, which passes off in vapour and is 
condensed in receivers ; it is not, however, pure, 
it is mixed with tarry matter, but from which it is 
easily freed by repeated distillation. In this state it 
is called pyroligneous acid^ from the Greek word 
pur ^ fire, and the Latin one lignum^ wood^ signify- 
ing the acid generated from wood by the action 
of fire. It is then a transparent colourless fluid, 
having a much sourer taste, but by no means the 
pleasant flavour of common vinegar. What is left 
in the cylinders is charcoal, and perhaps the purest 
kind of it that can be procured. 

PUTREFACTION. 

Almost every kind of vegetable matter is liable 
to undergo putrefaction ; certain circumstances are, 
however, necessary for the commencement of this 
process, as the presence of moisture and a proper 
heat. The substance first acquires a mould on its 
surface, it emits a disagreeable smell, and in the 
dourse of time is almost entirelv consumed. That 



PUTREFACTION. 303 

moisture is necessary for the matter to putrefy is 
evident, for if it be exposed to a high temperature, 
which drives off the watery part, it may be kept any 
time without putrefying. The temperature to which 
it should be exposed to make it undergo the putre- 
factive process, must therefore be such as will not 
expel the moisture, and the admission of air also 
favours the decomposition ; the ingredients being 
dissipated in thfe form of new aeriform fluids. Many 
substances, however, particularly those in which 
there is a large proportion of charcoal, are not con- 
sumed ; there remains a black matter called vegeta- 
ble mouldy which, when excluded from the air, does 
not putrefy, but soon does so when exposed to the 
atmosphere. Vegetable mould forms a principal 
pari of the soil, and contributes in no small degree, 
when properly treated, to vegetation, for which pur- 
pose the earth requires to be frequently turned up, 
to expose the mould, and allow putrefaction to go on, 
by which the matter probably passes into that state, 
that it is easily dissolved by w^ater, and is thus taken 
up by plants, and affords them nourishment. When 
this is not done, and when the vegetable matter 
mixed with the soil is in large quantity,^! collects, 
and forms /?ea/ and morass. When vegetable mat- 
ter is buried, the product of putrefaction is different. 
Owing to the absence of air, and to the pressure, 
little of the aeriform fluids is generated, and the 
decomposition goes on slowly. If the body contain a 
large quantity of carbon, w^hat remains retains a great 
deal of it, and a matter is left, which is not liable to 
putrefy, and differing in appearance from that from 
which it was formed. Hence most probably the 
origin of coal ; and that this is really the method by 
which it is formed, seems to be proved by the fact, 
that bodies have been found, which at one end are 
wood, and at the other are coal, the intervening sub- 
stance gradually appearing to change from the one to 
the other. 



304 ELEMENTS OF CHEMISTRY. 

The uses of coal, as a means of generating heat, 
are well known, {Seep, 111); but besides this, it is 
now employed largely in the manufacture of coal f^as. 

When coal is subjected to a strong heat, a large 
quantity of aeriform fluid is given off, now called coal 
gas, consisting chiefly of olefiatlt gas, carburetted 
hydrogen, and hydrogen along with carbonic acid, 
and sulphur in union with hydrogen and ammonia. 
When this is purified, it afibrds, during combustion, 
a steady light, and hence its use in lighting streets 
and apartments. For generating the gas, the coal, 
reduced to small pieces, is thrown into long cylin- 
ders of iron, previously brought to a red heat, in 
which it quickly undergoes decomposition, and the 
gas is given ofl", the ends of the cylinders through 
which the coal was introduced being then closed by 
means of a lid secured by a screw, and luting. Coal, 
like other vegetable matter, consists of carbon, 
oxygen, and hj^^drogen, but in addition to these, it 
also contains nitrogen, so that we can easily account 
for the formation of the gaseous products. Part of 
the carbon and oxygen unite to form carbonic acid, 
part of the carbon and hydrogen, by their union, 
form olefiant gas and carburetted hydrogen. The 
nitrogen comes ofl' in combination also with hydro- 
gen, forming ammonia, while the sulphur is also in 
union with hydrogen, constituting the compound 
called sulphuretted hydrogen. 

In this part of the process, it is of particular im- 
portance to pay attention to the heat applied to the 
retorts. If coal be put into a cold cylinder, and then 
heated, very little gas is procured, and nearly the 
same happens if it be thrown into it when previously 
heated to whiteness. When, however, it is thrown 
into it brought to a bright cherry heat, it instantly 
yields a large quantity of good gas, which, issuing 
from the open end of the retort, is conveyed through 
tubes into the condenser^ and from it into the puri- 
fier^ from which it proceeds to the gas holder. The 



COAL GAS. 



305 



first of these is merely a vessel filled with cold water, 
through which the gas is made to pass, and in which 
it deposits a large quantity of tar, and essential or 
volatile oil. The purifier through which it next 
travels, is a large apparatus filled with lime and 
water, the lime combining with the carbonic acid 
and sulphur, the former of which diminishes the illu- 
minating power of the gas, and the latter gives it an 
ofiensive smell, and makes it injurious when burned 
in apartments, more particularly to plated goods and 
" J"E? P^i^tings ; a, is a purifier of a simple 

form, 6, is the induction pipe passing 
to the bottom, and open below ; c, 
is the exit pipe, by which the gas is 
carried to the gasometer. By this 
means the gas, flowing through 6, is 
conveyed to the bottom of the fluid, and afterwards 
rises through it, so that its impurities are removed 
by the lime. The gas holder, into which it next 
passes, is a large vessel 
made of sheet iron, a, open 
below but shut above, and 
suspended in a tank of wa- 
ter, b 6, by means of chains 
which pass round pulleys, 
and have counterpoises, c 
d, for the gas holder fixed 




^1 



ez. 



a 



f 



W 



==i],P^ to the opposite end ; 6, is 
the induction pipe passing to the top of the tank,/*, 
g is the exit pipe. When the coal is put into the 
retorts, the gas holder is sunk in the water, and as 
the gas flows into it, it gradually raises it, and fills 
it, the counterweights preventing it from exerting 
much pressure on the gas. As, however, the gasom- 
eter, is not completely counterpoised, the moment 
the stopcock of any tube coming from it is opened, 
the gas is forced out by the gasometer falling in the 
tank. Of course the pressure to be given depends 
entirely on the distance to which the gas is to be 
26^ 



306 ELEMENTS OF CHEMISTRY. 

conveyed, and the number and size of the tubes- 
through which it has to pass. 

When coal gas, properly purified, is heated in con- 
tact with air, it burns with a bright white flame mixed 
with blue near the burner; the products of the com- 
bustion are carbonic acid and water, the oxygen 
combining With the carbon to generate the former, 
and with the hydrogen to produce the latter. Difier- 
ent statements have been given of the illuminating 
power of coal gas. Of course it must vary according 
to its mode of manufacture, and the coal from which 
it is procured ; a great deal must also depend on the 
method of burning it. An Argand burner, No. 2, 
of Edinburgh, and which consumes rather more than 
three cubic feet of gas per hour, when burning with 
a proper flame, about 3 incl>^s, gives in general alight 
equal to that of about 12 tallow candles (short sixes) 
burning with a clear flame, making each foot of gas 
equal to about 4 candles. 

It has been already said, that in the condenser tar 
and an essential oil are deposited. These are sold 
to refiners, who separate them by distillation. The 
latter is distilled over, and collected in receivers, 
and is now much used for dissolving caoutchouc, the 
former, which is left in the still, is used for cover- 
ing the roofs of houses and wood work. (See 
Caoutchouc and Tar, J Besides these there is also 
a large quantity of ammoniacal fluid procured during 
the decomposition of the coal, and which is sold to 
manufacturers of sal ammoniac, as from it they pro- 
cure ammonia, which is made to unite with muriatic 
acid, {See SalJimnioniac) After the whole of the 
gas is driven ofi', there remains in the retorts a black 
inflammable matter; it is coke, and is either used 
for heating the retorts, or sold to confectioners and 
others, in whose processes coal would prove injuri- 
ous from the smoke it gives out. 

A familiar method of shewing the production of 
inflammable gas from coal, is to fill a tobacco pipe 



SUGAR. 307 

with it, cover it with putty, and place it in a fire. 
In the course of a few minutes a dense white smoke 
appears at the mouth of the pipe, and which, on 
applying a flame, is kindled, and continues to burn 
for some time. 



VEGETABLE PRINCIPLES. 

The elements of the vegetable kingdom enter into 
union, and form what are called Vegetable Principles. 
Some of these are contained in all plants, while 
others are afforded by particular vegetables only* 
Some also are dispersed through the whole plant, 
while others occur only in certain parts. Those with 
which we are most acquainted are, Siigar^ Gunij 
Starchy Gluten^ Wax, Oils^ Resin, Caoutchouc^ 
and Tannin, with the Colouring Matters. 

SUGAR. 

This substance, so familiar from its general use, 
has been long known, but it was not till after the 
discovery of America that it was introduced to 
Europe as an article of food. When pure it is white. 
It is not altered by exposure to dry air, but in a 
damp atmosphere it becomes moist. When heated 
it melts, and swells ; and if the temperature be high, 
it takes fire, and burns with great violence. It is 
very soluble in water ; the solution, when strong, is 
thick and adhesive, and is much used under the name 
of syrup, for preventing vegetable bodies from decay- 
ing. A weak solution, on the contrary, very soon 
undergoes decomposition. 

Sugar is obtained from the juice of the sugar cane, 
growing chiefly in the West India Islands. It con- 
sists of water holding sugar dissolved in it, a mucila- 
ginous matter, and essential oil, and along with these 
there is mixed pieces of the cane and leaf, and other 



308 ELEMENTS OF CHEMISTRY. 

impurities^ all of which it is the object of the process 
ses to which it is subjected to remove. By passing 
the cane between rollers, the juice is extracted, after 
which it is put into large boilers, and brought to a 
boiling heat, and then mixed with slaked lime, the 
use of which is to neutralize any acid that may exist 
in it. After being kept near a boiling heat for some 
timOj the clear fluid is drawn off into evaporating 
basins, and evaporated as quickly as possible, the 
scum being removed as it rises to the surface, and 
the boiling continued, till it becomes of such consis- 
tence that it will crystallize on cooling. It is then 
poured into wooden troughs, in which it deposits 
small crystals, surrounded bj^ a brownish fluid. The 
crystalline mass thus obtained is put into hogsheads, 
in the bottom of which there are a number of holes, 
loosely stopped with the stalks of plantain leaf. 
These are placed over a large cistern, which is to 
collect the Tuolasses or treacle that drops from the 
sugar, and after it has dripped for two or three weeks, 
it is nearly dry, in which state it is imported to this 
country, under the name of muscovado or raiv 
sugar. 

Raw sugar contains impurities, from which it is 
freed by the process of refining, practised almost 
always in Europe. For this purpose, it is dissolved 
in lime water, and after being brought to a boiling 
heat, has bullock's blood mixed with it, which is 
instantly coagulated, and entangles any foreign mat- 
ter floating in it, and which is skimmed off, as it rises 
to the surface ; at the same time the lime neutralizes 
any alkali that may have been left in the preceding 
process. After this it is filtered through blankets, 
and boiled down to the proper consistence, great care 
being taken not to apply too strong a heat, otherwise 
it acquires a dark colour. It is then put into coolers, 
where it is allowed to thicken, in which state it is 
poured into unglazed earthen vessels, of a conical 
shape^ with their smaller ends down, and having a 



GUM. 309 

hole in them, stopped with a plug of clay, but which, 
after the evaporated juice has become solid, is remov- 
ed, and the unconsolidated part is allow^ed to drip 
through for some hours; a piece of wet clay is then 
put on the upper or broad end, the water of which 
passes through the sugar, and carries out the im- 
purities, the process being repeated till the whole 
of ihem are removed. When the claying is finished, 
the sugar is hardened, by heating it in a stove-room, 
and is then called loaf or refined sugar. It some- 
times also undergoes a second, or even a third puri- 
fication, and is then called double or /r2p/e refined. 

The juice that passes through during the claying, 
contains a considerable quantity of sugar, and is 
therefore subjected to the process of refining along 
with the other, but it is sometimes also refined 
alone ; the juice that passes through from it is com- 
mon treacle. 

GUM. 

Similar in many of its properties to sugar, is gum, 
of which there are difierent kinds, but the principal 
is gum arable^ the produce of trees growing chiefly 
in Africa, Arabia, and parts of Asia. From these 
it exudes in a liquid state either spontaneously, or 
from incisions made in the bark, and becomes hard 
by exposure to air. 

It is usually in small irregularly formed pieces, of 
different colours, soine being brownish, others yel- 
low, and some almost colourless, the last of w^hich is 
considered the best ; hence it is often separated from 
the others, and sold under the name of picked gum. 
Gum is soluble in water, forming a solution called 
mucilage^ the consistence of w^hich varies according 
to the quantity dissolved. It is insoluble in alcohol, 
hence, owing to the strong attraction existing between 
these fluids, when the latter is added to mucilage, it 
unites with the water, and the gum is deposited in 



^10 ELEMENTS OF CHEMISTRY. 

the form of a white powder. Besides gum arable^ 
there are others differing a little from it. Cherry- 
trees, and many others of this country, yield it in 
considerable quantity. Tragacanthj though called 
a gum, is by no means so, as it differs from it com- 
pletely in its properties. It is the produce of certain 
kinds of trees growing chiefly in Persia. It exudes 
from them in its fluid state, but gradually becomes 
solid. It is insoluble in water, in this respect differ- 
ing from gum. When mixed with it, it becomes 
soft, and swells ; and if the quantity of fluid be great, 
it is diffused through it, thus appearing to form a 
solution, but from which the tragacanth separates on 
being left at rest. 

Gum is chiefly employed from its power of sus- 
pending substances in water, when not soluble in it ; 
hence its use in calico printing, in dyeing, and in 
making ink, the gum keeping the colouring matter 
suspended in the water. It is also used for stiffen- 
ing linen, and to cause substances to adhere. 

STARCH. J 

When wheat flour is put into a large bag and 
kneaded with water, it is separated in two distinct 
parts ; a tough elastic substance remains in the bag, a 
white powder passes through, which is starch. 

Starch is insoluble in cold, but soluble in warm 
water^ and if the quantity of starch be great, a thick 
solution is formed, which gelatinises on cooling. If, 
however, the solution is weak, tbe starch still con- 
tinues dissolved, though the temperature falls. 

Starch exists in a great many vegetables, particu- 
larly in the seeds and roots of almost all those used 
as food, as in the different kinds of grain, in rice, 
peas, beans and potatoes, and the nearer these are to 
maturity the more they contain. That from which 
the best is procured, is wheat. For thia purpose it 
is bruised, and kept in cold water for about a fort- 
night, during which it undergoes fermentation, and 



STARCH. 311 

emits an unpleasant smell. It is then mixed with 
water, till the pulpy matter becomes so thin, that it 
can be passed through a hair sieve, by which the 
husks are removed, and the filtered fluid allowed to 
remain at rest, till the starch is deposited. It is not, 
however, pure ; it is therefore again treated in the 
same way, and afterwards put into boxes, having 
the bottoms perforated, and lined with linen cloth, 
through which the water parses, and leaves the starch 
behind. When it has become of sufficient consis- 
tence, it is cut into small pieces, and dried by a 
stove, during which they crack, and form the small 
irregular pieces. 

Starch is the principal vegetable matter from which 
nourishment is derived; hence it is employed largely 
as food, as in the diffeient kinds of grain, potatoes, 
and many others. Sago and arrow-root are almost 
entirely compo.sed of it. It is used also for stifiening 
cloth, for which purpose it is first thoroughly mixed 
with a little cold water, and then with boiling water, 
by w^hich a solution is procured, to be afterwards 
diluted according to the stiffness to be given to the 
cloth. 

In the process of making starch from wheat, after 
removing the husks, the future steps are merely to 
wash off the starch from the other substances exist- 
ing in the grain. What remains in the first washing 
on the sieve is cdWed ghiten. 

Gluten is a tough elastic substance, of a whitish 
colour, and very adhesive. It exists in different 
quantity in different bodies, but some of those which 
yield starch, do not contain any, such as potatoes; 
and as it is necessary in the making of bread, those 
which do not afford it, do not answer well for this 
purpose. 

The substances used in making bread, are wheaten 
flour, water, yeast, and salt. The proportions vary 
in different places, not only on account of the quality 
of the flour, but also owing to the temperature of the 



312 ^ELEMENTS OF CHEMISTRY. 

place. The quantity to be baked also makes a differ- 
ence in the proportions, for the greater the quantity 
of flour, the less yeast it requires. The proportion 
of salt depends in a great measure on the taste of 
the baker. In general the yeast, with the salt, and 
about half of the water and flour, are first mixed 
in a wooden trough and kept in a warm place, 
during which the glutinous principle in the flour, 
being acted on by the yeast, begins to undergo fer- 
mentation, by which it becomes sweetish, and disen- 
gages carbonic acid gas, the greater part of which, 
owing to the adhesive quality of the mixture, is 
prevented from escaping ; it therefore causes it to 
swell, and become spongy, hence the product is call- 
ed by bakers a sponge. Having been kept for about 
10 or 12 hours in this situation, it is again put into a 
trough, and mixed with the remainder of the flour 
and water, by which the fermentation is stopped, 
but it again very soon commences. The substance 
thus formed, called doughy is kept in the trough for 
about an hour, during which the fermentation pro- 
ceeds, carbonic acid gas is again generated, and being 
retained, causes the mixture to swell considerably. 
Were the mixture to be allowed to remain in the 
trough, the fermentation would proceed, and it would 
become sour. It is necessary, therefore, to put a stop 
to it." For this purpose, the dough is cut into loaves 
of the requisite size, and then put into an oven, and 
exposed to heat for about an hour, by which part 
of the moisture is expelled, and the fermentation 
ceases. 

It has been mentioned, that those substances which 
contain little or no gluten do not answer for making 
bread, because, as it is it that occasions the fermen- 
tation, and consequent disengagement of gas, the 
bread made of them is not at all porous. A certain 
degree of porosity may, however, be communicated, 
by mixing these substances with others that contain 
gluten. 



WAX. S13 



WAX. 



TVax^ though prepared by bees, is undoubtedly of 
vegetable origin, and seems to be formed by some 
change which sugar undergoes. When pure, it is a 
white solid substance, brittle at a natural temperature, 
but soft and tenacious when heated, and without taste 
and smell. Common bees' wax, however, is yellow, 
and has a pleasant odour, but these are owing to im- 
purities, both of which it loses by purification. It 
becomes fluid at about 140, and is one of those bodies 
which pass through different degrees of consistence 
during its passage from solid to fluid. When the 
heat to which it is exposed is high, it takes fire, and 
burns with a bright white flame. 

Wax is not soluble in cold alcohol, but on the 
application of heat it is dissolved; hence the use of 
warm spirit for removing spots of wax from cloth. 
It is also dissolved by oil of turpentine, and this is 
likewise much used for removing it from cloth, the 
disagreeable smell left by the turpentine being easily 
banished by lavender water. 

Wax is principally employed for affording light. 
The superiority of wax over tallow candles, depends 
on the former not being so fusible, and hence requir- 
ing a smaller wick. In the latter, the matter melted 
by the heat is much greater ; a large wuck is there- 
fore necessary for drawing it up, which being placed 
in the centre of the flame, is excluded from the air, 
and is not consumed ; unless, therefore, it is fre- 
quently removed, it obstructs a great deal of the 
light. The small wick of a wax candle, on the con- 
trary, is suflicient to draw up the melted matter; it 
obstructs less light, and, though excluded from the 
air by being surrounded by the flame, yet, when it 
becomes long, it bends, and thus the end getting 
without it, is exposed to the air, and consumed, so 
that it does n6t require to be snuffed. 
27 



314 ELEMENTS OP CHEMISTRT. 

Wax is -likewise employed in taking casts and 
moulds, for which, from its softness when a little 
heated it is well adapted. It is also a principal ingre- 
dient in some kind of luting, {See page 217.) 

OILS. 

Oils have been divided into two classes, ihe fixed 
or unctuous^ and the volatile or essential. The 
former, of which an immense variety exists, are gene- 
rally fluid, but of a thickish consistence ; they are 
sometimes colourless, occasionally of a greenish or 
yellow colour, and when pure, are transparent, and 
in general free from smell. When paper is dipt into 
oil, it acquires a greasy stain, and which is removed 
with difficulty ; perhaps the best method is, to place 
a sheet of blotting paper above and below it, and 
over the whole another piece of paper, with some 
finely powdered chalk, and by the application of a 
warm iron, the oil is melted and absorbed. 

When oil is kept for some time, particularly if 
exposed to the air, it becomes thick and rancid, and 
if spread on cloth or paper, becomes solid. Some 
oils, when in this state, are opake, others are trans- 
parent. To the former, which are called fat oils, 
belong those obtained from linseed, nuts, poppies 
and hemp-seed; to the latter, termed dryings olive 
oil, oil of almonds, and rape seed. 

It has been said, that when oil is exposed to air, it 
becomes thick, which is owing to the absorption of 
oxygen. Under certain circumstances, this change 
goes on so quickly, that the heat generated by the 
condensation of the gas is sufficient to set the oil on 
fire. When, for instance, tow or cloth is soaked in 
oil, and heaped together, it is in general very soon 
kindled. 

When oil is heated in. air to a proper temperature, 
it burns with a yellowish flame. For complete com- 
bustion, the heat must be such, as is more than suffi- 



SOAP. 315 

cient to convert the oil to vapour; but when the 
heat becomes much higher, by which the oil is quick- 
ly drawn up, there is not a sufficient supply of 
oxygen, and the whole is not consumed. {See Com- 
bustion^ page 110.) 

The most important action of oils is with alkaline 
matter, with which they combine, and form soap. 

Before proceeding to detail the process of soap- 
making, it may be here remarked, that there exists 
in animals an oily matter, the consistence, colour, and 
smell of which, vary according to the animal from 
which it is procured, but in its general properties, 
combustibility, and power of forming soap with alka- 
lies, it is the same. Tallow, though solid at a natural 
temperature, must be considered also merely as an 
animal oil. 

The substances used in the manufacture of soap vary 
according to the kind to be made. For the finest white 
soap, olive oil and soda are employed. Common 
white soap is prepared from tallow and soda, instead 
of which, potassa and sea salt are sometimes used ) 
and yellow soap is made of these substances and rosin. 
When oil is mixed with soda, the soap is hard, but 
with potassa it is soft; if, however, sea salt be added 
to the latter during its preparation, it makes it of the 
same hardness as the other, the potassa uniting with 
the muriatic acid of the salt, and setting free the soda, 
which acts on the oil. When, then, owing to the 
expense of kelp and barilla, or to other circumstan- 
ces, soda cannot be procured, potassa and sea salt are 
employed. 

In making common soap, the alkaline matter, say 
kelp or barilla, is dissolved in water, and mixed with 
lime, which is to unite with the carbonic acid, form- 
ing an insoluble compound, and setting the soda' free ; 
the solution, after being drawn off, is evaporated to 
the proper consistence, in which state it is called a 
ley J and is ready for receiving the oil. The tallow, 
after being melted, is poured into it, and the whole 



316 ELEMENTS OF CHEMISTRY. 

is boiled so as to cause them to unite. The fire is 
then extinguished, and the materials left at rest for 
some time. Sea salt is next added, and heat again 
applied, and more alkaline solution put in, and in 
this way the process is carried on, till the whole of 
the solution and tallow is used, the watery part being 
drawn off as it is separated from the soap, at the same 
time the boiling is continued, till it becomes of the 
proper consistence, after which it is poured into th^ 
frames to harden. These are wooden troughs with 
moveable bottoms, into which the soap, while still 
fluid, is poured, and in which it remains for some 
days, till it becomes so hard, that it can be handled 
without being broken ; it is then removed, and cut 
into oblong pieces, by means of a wire or string, and 
placed in well ventilated apartments to dry. 

It has been said that sea salt acts when potassa is 
used, by its being decomposed, and setting soda free; 
it serves, however, another purpose. It is supposed 
to combine with the watery part, and remove it from 
the soap, which thus becomes sooner hard, and con- 
sequently the process is considerably shortened. If 
potassa be used without the addition of sea salt, the 
soap formed does not become hard ; and hence the 
method of making soft soap. The oil generally em- 
ployed is linseed, hemp, or rape oil. It is mixed 
with a strong alkaline solution, obtained from pot- 
ashes or pearlashes and lime, and after being thor- 
oughly incorporated, the mixture is boiled till the 
soap becomes of the proper consistence. 

Soft soap is usually of a brown colour, is much 
stronger and more acrid than the other. When well 
made, it is of the consistence of thick paste, and 
should be entirely soluble in water, forming a white 
froth. It is employed chiefly for scouring woollen 
stuffs. 

Common yellow soap is made with the solution 
procured from kelp or barilla, and tallow, to which, 
after they are sujfficiently mixedj, melted rosin^ aad 



SOAP. 317 

occasionally a little palm oil, is added. The subse- 
quent parts of the process are the same as have been 
already described. 

Marbled soap is prepared by adding to the mate- 
rials, after they have been properly boiled, an alkaline 
solution, immediately afterwards green vitriol, by 
which the latter is decomposed, and a dark coloured 
precipitate is formed, that is partially mixed with 
the soap. The materials are then allowed to cool, 
and become hard, and the spent ley is drawn off. 
The soap after this is again melted, and colcothar, 
made into a paste with water, is gradually added, and 
the whole is stirred, but so as to mix the powders 
imperfectly, and when this is done, it is poured into 
moulds. Owing to the repeated heating to which 
this kind of soap is submitted, it is much harder than 
the others, and therefore not so easily dissolved. 

Soap prepared by any of these processes, does not 
possess either the corrosive quality of the alkali, nor 
the greasinessof the oil; water, when pure, dissolves 
it, but if it contain an earthy salt in solution, it is not 
dissolved, but decomposed. Hence the cause of the 
hardness of water, which is owing in g^eneral to the 
presence of a salt of lime, the acid of which unites 
with the alkali of the soap, the oily matter being set 
free. If we attempt to dissolve soap in hard water, 
white flocculi are formed, and it has a disagreeable 
feel ; hard water does not therefore answer for w^ash- 
ing with. The hardness of water may in a great 
measure be removed, by boiling it for some lime, 
and by the addition of a little potassa or soda, which 
decomposes the earthy salt, and prevents the decom- 
position of the soap ; but even with these addi- 
tions, it is not so good as soft water. 

Oil combines with the earths, and forms soaps, 
which differ from those containing the alkalies, in 
not being soluble in water. When lime water is 
mixed with oil, a soapy substance is formed, well 
known by the name oicarron oil ; so called from its 



318 ELEMENTS OF CHEMISTRY. 

being much employed at the Carron iron works as a 
cooling application to burns. It is prepared by mix- 
ing equal quantities of lime water, and olive or lin- 
seed oil. Oil exerts little action on metals, hence 
the usual practice of besmearing metals with oil, to 
prevent them from being rusted. In some instances, 
however, it causes them to undergo a change, as is 
particularly the case with copper, which, when be- 
smeared with it, acquires a greenish crust. 

The fixed oils are found in great abundance in a 
variety of plants, chiefly in the seeds and fruits, and 
the nearer they are to maturity, the greater is the 
quantity. They are obtained from them either by 
squeezing them in a press, or by boiling them in 
water ; the oil being separated from it as it floats 
over it. 

Oil is employed for aflbrding light. Drying oil 
is used in the composition of paints and varnishes ; 
but before being mixed with the paint, it undergoes 
a process, which makes it dry more easily. For this 
purpose it is boiled for some time, during which it 
becomes thicker, and of a darker colour. It is occa- 
sionally set on fire, and allowed to burn for a short 
time, and after the flame is extinguished by putting 
on the lid of the pot, it is boi4^d, till it becomes of the 
requisite thickness. It is sometimes also boiled with 
litharge, by which it undergoes a slight decomposi- 
tion. By all of these processes, it loses its greasi- 
ness, and is thus rendered fit for the purposes of 
painters, and for the preparation of varnishes. For 
the former, it is mixed with white lead, and then 
with the paint ; and for the latter, with oil of turpen- 
tine and resin. Those made in this way differ from 
spirit varnishes, in being much more flexible when 
dry, and of course not so liable to crack. 

Drying oil is likewise used by printers. Nut oil 
is considered the best for black ink; and for other 
colours, that from linseed is commonly employed. 
In preparing them the oil is merely subjected to the 



OIL GAS. 319 

process of boiling, already mentioned, and is then 
mixed with the requisite quantity of 4am p black. 
During this process, it is evident that it must undergo 
some changes, for it adheres easily to moist paper, 
which it would not previously do. 

Oil is now much employed also for yielding a gas, 
used as a means of affording light. 

When oil is subjected to a red heat excluded from 
the air, it is decomposed, its elements enter into a 
new state of combination, and a large quantity of 
gaseous matter, now called oilgaSj is given ojff, which 
aflfords by its combustion a very brilliant light. It 
is a mixture of olefiant gas and carburetted hydrogen, 
and from the large quantity of the former which it 
contains, it is of superior illuminating power to coal 
gas. As oil is composed almost entirely of carbon 
and hydrogen, the proportion of oxygen being very 
small, little or no carbonic acid is contained in the 
gas, and it is entirely free from sulphur. For this 
reason, it does not require to be purified ; hence the 
method of preparing it is much more simple than that 
for procuring coal gas. All that is necessary is to 
allow the oil to flow into a red hot cylinder, by which 
the gas is formed, and conveyed to the gasometer. 
For this purpose a reservoir full of oil is connected 
by a tube with a cast iron retort, placed in a furnace, 
and from the opposite end of which there pass tubes 
to the gasometer. Having stuffed the retort v/ith 
pieces of brick or coke, it is brought to a red heat, 
and the oil is then allow^ed to flow in, in a small 
stream, the use of the coke or brick apparently being 
merely to retard its progress, and thus expose it 
more completely to heat. The moment it enters the 
retort, it is decomposed, gas is formed, and passes 
into the gasometer. During its passage through the 
tubes, it deposits a little volatile oil and acetic acid, 
which are easily draw^n off by a stopcock attached to 
them, but it still retains part of the former, which 
«;ives to it its peculiar odour. 



320 ELEMENTS OP CHEMISTRY, 

The quantity of gas given off from oil varies 
according to the heat; 100 cubic feet maybe got 
from a gallon, but it seldom amounts to so much ; in 
general 80 may be considered an average quantity. 
More may, however, be procured, but in this case it 
is of very inferior illuminating power. 

Different statements have been given of the com- 
parative power of illumination of oil gas, and this 
has been occasioned in a great measure by the differ- 
ence in its properties, owing to the method followed 
in procuring it, as it has been already mentioned, that 
the more there is obtained from a given quantity of 
oil, the illuminating power always becomes less. 

It has been found from numerous trials, that a foot 
of oil gas will afford a light equal to that of about 
from 6 to 8 tallow candles (short sixes), burning with 
a clear flame, supposing the quantity obtained from 
a gallon of oil to be about 80 feet. This makes the 
illuminating power to be about double that of coal 
gas bulk for bulk. 

An easy method of procuring oil gas on a small 
scale is to put some oil into a funnel, a, having a 
stopcock, b, and attach- 
ed to a tube, c, passed j ^ \^j 
through a chauffer to ^^Wkm^ \^^ 
bring it to a red heat. 
The opposite end, e, is 
connected by a tube with 
a gas holder. When the 
tube, c, is properly healed, the stopcock, b, is open- 
ed and almost immediately shut, by which a little 
oil is allow^ed to flow in, and the moment it falls on 
the hot tube gas is given off, so that, by repeatedly 
turning the cock, a sufficient quantity may be form- 
ed to fill the gas holder. See Manual^ page 194. 

VOLATILE OILS. 

The volatile oils possess some of the properties of 
the fixed ones, but they differ from them in many 




VOLATILE OILS. 321 

respects. Their distinguishing character is their 
leaving a greasy slain on paper, but which is easily- 
removed byheat. Hence a method, not only of dis- 
tinguishing them from other oils, but also of knowing 
whether they are pure. Thus, if a drop of common 
oil be thrown on paper, and held near a fire, a part 
fiies off, but before the whole of it can be dissipated, 
the paper is destroyed. If, on the contrary, a few 
drops of any volatile oil, as turpentine, be thrown 
on paper, and treated in the same w^ay, the stain dis- 
appears, without the texture of. the paper being in 
the smallest degree injured. If the oil be not pure, 
that is, if it be adulterated with any fixed oil, which 
is frequently the case, particularly the more expen- 
sive ones, the spot does not entirely disappear ; the 
volatile oil flies off, but leaves the other. Owing to 
this property, volatile oils are sometimes employed 
for making paper transparent, with the view of copy- 
ing drawings. For this purpose, the paper is be- 
smeared with pure volatile oil of turpentine, and 
dried for a short time by exposure to air ; it is then 
put on the drawing, the traces of which are distinctly 
seen through it. After taking off the copy by a pen- 
cil, the oil is easily expelled by holding it near a fire. 

The volatile oils are in general as fluid as water, 
though they are occasionally thick. Some are col- 
ourless, but others are of a bluish or greenish colour. 
They have a hot taste, and each has a smell peculiar 
to itself. TJiey are generally lighter than water, and 
can be converted into vapour at a temperature below 
its boiling point, provided it be present, and the oil 
is not altogether excluded from the atmosphere. 

When exposed to the lij^ht. they become thick and 
dark coloure ' and are not so easily volatilized, hence 
the necessity of using recently prepared oil, for the 
experift:euts above enumerated. When heated in 
air, they burn with rapidity, and at the same time 
generate a great deal of smoke. Volatile oils are 
sparingly soluble in water, and communicate their 



222 ELEMENTS OP CHEMISTRY. 

smell and flavour to it ; hence the method of prepar« 
ing peppermint and cinnamon waters, merely by- 
distilling it from the vegetables that yield pepper- 
mint and cinnamon oil. 

Volatile oils act with great ease on acids, with 
some of which, indeed, the action is very violent. 
When oil of turpentine is mixed with a few drops of 
sulphuric acid, it becomes quite black, owing to the 
deposition of the carbon of the oil. With nitrous 
acid the action is very violent, the mixture almost 
instantly bursting into flame, and hence the necessity 
of great caution when mixing them. Thus, if about 
half an ounce of oil of turpentine be put into a galli- 
pot, and an equal quantity of nitrous acid previously 
mixed with a fourth part of oil of vitriol, in a phial, 
(tied to the end of a long stick,) be added to it, the 
action is accompanied with the disengagement of gas, 
which is instantly kindled. 

Essential or volatile oils are found in almost all 
the difierent parts of plants ; in each, however, they 
are contained in some particular part, though in a 
few instances they are dispersed through the whole. 
When in larger quantity, they may be obtained by 
subjecting the vegetable to pressure, but they are 
usually procured by distillation. For this purpose 
the vegetable, cut into small pieces, is put into a 
still with water, and heat is applied, by which the 
water and oil rise together in vapour, and are con- 
densed in the receiver. As there is no chemical 
attraction between them, they very soon separate, so 
that the oil is easily got pure. Some of the volatile 
oils, as turpentine, are procured by distillation from' 
resins. 

Volatile oils are used chiefly in the preparation of 
varnishes and paints. 

RESINS. 

Resins are solid brittle substances, generally of a 
brownish colour, having a slight degree of transpar« 



RESINS. 323 

ency and considerable lustre. They are usually 
without taste and smell, though they have occasion- 
ally both, but owing to impurities. When heated, 
they burn, giving off a great deal of smoke. They 
are insoluble in water. They are acted on by acids, 
but at the same time undergo decomposition. The 
substance that dissolves them most easily, is spirit of 
wine, but for this purpose it requires to be strong. 
The solution is transparent, and by evaporation 
affords the I'esin unchanged. By the addition of 
water to the alcoholic solution, the resin is deposit- 
ed, the water and alcohol uniting. In this respect 
they are opposed to gum, which is soluble in 
water, and the solution of which is decomposed by 
alcohol. 

Resins are soluble in oils, both the fixed and vola- 
tile ; thus, oil of turpentine easily dissolves them, 
and affords a solution which is also transparent. 

Resins are obtained from juices which exude from 
different kinds of trees, either naturally, or by making 
cuts in the bark. The fluid thus procured is a mix- 
ture of volatile oil and resin, which are separated by 
distillation, the former being driven off in vapour, 
the latter being left in the retort. They of course 
vary in their properties according to the tree from 
which they are procured. The most common are 
obtained from the varieties of fir, the juices of which 
are called turpentines. That of Scotch fir, when dis- 
tilled, yields common resin ; that of larch, Venice 
turpentine, and the Balm of Gilead fir, Canada bal- 
sam. The fluid procured by the distillation of these 
is oil of turpentine, or what is commonly sold under 
the name of turpentine. 

Other resins are obtained fVom different sources, 
as copal^ from a tree that grows in Spanish America, 
mastichj the produce of a tree which grows in the 
Levant, and lac, said to be a deposit from insects on 
different species of trees, natives of the East Indies, 
and many others. 



324 ELEMENTS OF CHEMISTRY. 

Copal is a white resin, with a slight tinge of brown. 
It is insoluble in water, and even in alcohol it is dis- 
solved with dijSiculty, in this respect differing from 
common resins. It may, however, be dissolved in 
oils, and it then forms a very fine varnish. When 
melted till it ceases to emit a peculiar odour, which 
it at first gives off, and then mixed with an equal 
quantity of linseed oil, previously freed of its colour 
by exposure to the sun's rays, it is dissolved, and is 
in this state used as a varnish. Four parts of copal 
melted, and afterwards mixed with oil of linseed, 
and about as much oil of turpentine as is equal to the 
whole mixture, form a varnish used by japanners. 

Copal, it has been said, is acted on with difficulty 
by alcohol, and the volatile oils; we are obiiged, 
therefore, \o have recourse to a particular manage- 
ment to get it dissolved. This may be effected by 
boiling it in them under an increased pressure, or by 
exposing it to their vapour, by which it is at first 
softened, and then dissolved. 

TAR. 

Tar is nearly allied to resin. It is a thick fluid 
of a brown colour, prepared from the wood of differ- 
ent, kinds of trees that afford turpentine. For this 
purpose, it is cut into pieces, and heaped up in an 
oven, in which it is kindled, and allowed to burn, 
though imperfectly, during which tar is formed, and 
falls to the bottom, and is carried off by means of 
tubes into casks. A fluid of nearly the same nature, 
is now prepared in those processes in which wood is 
subjected to heat, for the purpose of preparing char- 
coal and pyroligneous acid, and which is condensed 
in the cool part of ihe apparatus, {See page 153.) 
Pilch is merely tar burned to a proper consistence, 
the fluid which comes off being collected. For this 
purpose tar is put into a still, and heat gradually 
applied, during which an acid and an oily fluid are 
distilled ; the first is impure vinegar, the latter an 



cAouTCHoue. 325 

impure turpentine, and often employed for coarser 
sorts of painting; what remains in the still is pitch. 

CAOUTCHOUC. 

Caoutchouc^ or Indian Rubber, was first brought 
to Europe from America, about the beginning of the 
last century, but its history was not then known. It 
was not till about the middle of the century, that it 
was discovered to be the juice of a particular plant. 
Since then it has been found in other places, chiefly 
the East Indies. 

Caoutchouc, when pure, is white, but it is usually 
of a dark colour, owing to the method of preparing 
it. This is done by collecting a thin film of the juice 
on the mould, the form of which it is to take, and 
drying it, first by exposure to the sun's rays, and 
afterwards in smoke, successive layers being put on, 
til! it is of the requisite thickness. 

It is remarkable for its elasticity ; a small piece of 
i t may be stretched out to a great length, and the 
moment the extending force is withdrawn, it regains 
its formerdimensions. It is also peculiar in resisting 
the action of powerful chemical agents. It is not 
soluble in water, or in alcohol, and it is very little 
afiected by the acids and alkalies, unless they are 
concentrated, and aided by heat, in which case it is 
slightly corroded. The only fluids that dissolve it, 
are ether, and some of the volatile oils. For dissolv- 
ing it in the former, it ought to be previously softened, 
by boiling it for some time in water, and the ether 
should also be washed with water, otherwise it does 
not act on it. For this purpose the ether and water 
are put into a bottle, and shaken together; on allow- 
ing them to remain at rest for some time, they grad- 
ually separate, the ether, being the lighter, rises to 
the surface, and may be drawn off; and by far the 
easiest method of doing this, is to put the mixture 
into a funnel, or tube, the mouth of which is shut by 
a cork and wire ; on leaving them there a little, thiS 
28 



326 ELEMENTS OF CHEMISTRY. 

water sinks, so that there is a distinct line of separa* 
tion. The cork is then to be withdrawn, the water 
escapes, and must be allowed to do so till the ethergets 
to the mouth, which is then to be shut. To dissolve 
tbe caoutchouc, all that is necessary is to put it with 
the ether into a bottle, cork it tightly, and leave them 
together for some time. This solution, when exposed 
to the air, evaporates, and leaves the caoutchouc un- 
changed in its properties. 

Some of the volatile oils also dissolve caoutchouc, 
by far the most powerful of which is that now pro- 
cured by the distillation of coal tar, a substance form- 
ed in large quantity in making coal gas. This is the 
patent process of Tennant of Glasgow. About 12 
ounces of the caoutchouc cut into small shreds, are 
put into a wine gallon of the oil, kept warm by means 
of a steam bath, the mixture being stirred till it be- 
come a thin pulp, after which it is passed through a 
very fine hair or muslin searce. 

Caoutchouc, from its elasticity and power of resist- 
ing the action of the chemical agents, is well adapted 
for many purposes; hence its use in making flexible 
tubes and varnishes. From the difficulty of getting 
it formerly in solution, tubes used to be made by 
cutting it into long pieces, softening these by boiling 
them in water, and then wrapping them round a 
piece of cane, and beating them till they adhered. 
This method is, however, now little followed, as the 
caoutchouc is so easily dissolved bj'' coal tar oil, and 
.which is so volatile, that when exposed to the air, it 
flies off, and leaves the caoutchouc in its pure state, 
adhering to the substance on which it is spread. For 
making tubes, the solution is now applied to leather, 
or cloth, which is allowed to dry, and then wound 
round a cylinder, several coatings being afterwards 
given, by which the tube becomes quite air tight. 
It is in the same way that the solution is now used 
as a varnish, the oil flying off, and leaving the caout- 
chouc. Hence also the method of making water- 



TANNIN. 327 

proof cloth, shoes, bags for holding air, &c. For 
this purpose a piece of cloth is stretched on a frame, 
and besmearetl with the solution, and left exposed 
to the air till it becomes clammy. Another piece of 
the same size, treated in a similar manner, is put oii 
the other, and then passed between rollers, and dried 
in a warm room, during which the oil escapes, and 
leaves them adhering. 

TANNIN. 

The substances called nutgalls, besides other ingre- 
dients, contain a matter which has been long known 
to give a black colour with salts of iron, and to act 
powerfully on the gelatinous parts of animals. These 
properties are owing to their containing a peculiar 
principle which has been called tan or tannin^ from 
its use in the art of tanning. Tan is never prepared 
pure for use in the arts; it is always employed mix- 
ed with other substances derived from the bodies 
from w^hich it is obtained. It is contained in a great 
many vegetables. That which yields it in largest 
quantity is nutgalls, excrescences which grow on the 
leaves of oaks, occasioned by the puncture of a small 
insect. They are of a roundish form, are very astrin- 
gent, and have a disagreeable bitter taste. Tannin 
exists also in the leaves and bark of many vegetables. 
The bark of oak, of Leicester willow and Spanish 
chesnut. Souchong and green tea, and Sumac, the 
branches and leaves of a tree that grows in Spain and 
the Levant, contain it in considerable quantity. It 
has been found that the inner bark has more than 
the outer ; accordingly young trees, in which the 
former predominates, yield most. The substances 
called kino and catechu, contain also a very large 
quantity of it, the" catechu from Bombay yielding 
upwards of half its weight. 

Tannin, it has been already said, gives a black 
colour with the salts of iron, hence its use in making 
inj^. {See page 247.) It acts also powerfully on 



328 ELEMENTS OP CHEMISTRY. 

some kinds of animal matter, as skin, and hence its 
use in making leather. (See Gelatin.) 

For the method of knowing the value of astrin- 
gent matter^ (See Leather.) 



ANIMAL SUBSTANCES. 

Animal, like vegetable matter, undergoes sponta- 
taneous changes, but it seldom passes through all the 
states of fermentation ; the most common is putre- 
faction^ which very quickly commences, provided it 
be exposed to a proper temperature and moisture. 
The nearer the former is to 90, the more speedily 
putrefaction takes place, if the temperature fall below 
30, it ceases entirely. Moisture is also necessary, 
and a free admission of air The first effects are, a 
change of colour and consistence. The matter, say 
flesh, becomes paler and softer, and emits a disa- 
greeable odour, accompanied with the disengagem.ent 
of aeriform substances. After this has gone on for 
some time, it becomes dry, and ceases to have the 
offensive smelL 

Various means are resorted to for retarding animal 
putrefaction ; a reduction of temperature is by far 
the most eflicacious. Meat, when put into snow or 
ice, may be kept almost any length of time, and hence 
the common practice of sending fish to a distance, 
packed in ice. In cold countries, also, a store of 
provisions is laid up, surrounded by snow, in which 
st3te it remains till required for use. Depriving 
animal matter of its moisture, is another mode of 
preventing putrefaction. We find accordingly, that 
dried fish may be kept for a^lOng time. In some 
countries, it is also the custom to cut flesh into thin 
slices, and dry it gradually, by which it may be pre- 
served till provisions cannot be otherwise procured. 
There are many substances which retard putrefaction^ 



GELATIN. 32B 

and some of which it is supposed act merely by ab- 
sorbing the moisture of the animal matter. The 
most powerful of these is common salt, which is used 
in great quantity for preserving butcher's meat, fish, 
butter, and many other articles. Of late pyroligne- 
ous acid has been highly recommended for this pur- 
pose. It is even said that it will render sweet, 
animal matter that has become putrid. In using it, 
the meat is merely dipped into it, and almost instant- 
ly removed. Should it have become putrid, it may 
be left in it for a few minutes. 

Other means have also been practised for prevent- 
ing putrefaction. The complete exclusion of air, it 
is well known, retards it; hence the custom of rub- 
bing eggs with butter, and of keeping them in lime 
water. Flesh is also sometimes preserved in this 
way. For this purpose, it is put into a cask, vvhicii 
is afterwards made as air tight as possible. It has 
been found also, that by boiling meat for some time, 
and then putting it into barrels, it may be kept long 
without putrefying, and hence a practice often resort- 
ed to by those going long voyages^ 



ANIMAL PRINCIPLES. 

In animal as in vegetable matter, there are sub- 
stances called animal principles, possessed of pecu- 
liar properties, and which are applied to useful 
purposes in the arts. The chief of these are Gelatin 
and Albumen. 

GELATIN. 

When part of an animal substance, particularly 
skin or cartilage, is boiled in water, after having 
been previously well washed, a fluid is obtained, 
which, when evaporated, and allowed to cool, con- 
geals; forming a substance called Gelatin qv Jdly. If 



330 ELEMENTS OF CHEMISTRY. 

this be heated it becomes liquid, the water is driven 
off, and it is thus procured in a state of purity. 

When gelatin is put into cold water, it softens and 
swells, but is not dissolved ; it is necessary to heat 
it, by which a solution is formed, differing in con- 
sistence according to its strength. By far the most 
important action of gelatin, is with the astringent 
matter of vegetables. When an infusion of nutgalls, 
oak bark, or willow bark, is added to the solution of 
gelatin, a powder is precipitated, or if the solution 
be strong, a tough matter is formed, which is a com- 
pound of the vegetable and animal principles, and 
which becomes hard on being kept. On this de- 
pends the art of tanning, or the making of leather, 
which is merely the union of the astringent matter 
in vegetables, with the gelatinous principle existing 
in the skins, by which they are gradually converted 
to a substance insoluble in water, and not liable to 
undergo decay. 

The previous steps, in preparing skins for convert- 
ing them into leather, consist in removing the hair, 
fat, and other impurities, after which they are sub- 
jected to different processes, according to their nature, 
and the kind of leather required, as tanning, or caus- 
ing them to unite with astringent vegetable matter, 
tawing, or making them imbibe alum and other salts, 
with some animal substance, and ciLvrying, or soak- 
ing them in oil to make the leather soft, and imper- 
vious to water. These processes are often performed 
on the same skin, by which the leather is fitted for 
more purposes. The thick hides of which the soles 
of shoes are made, are merely tanned, while the 
white kid glove leather is tawed. That for the upper 
leather of boots and shoes, is both tanned and curri- 
ed, and the fine Turkey leather is first tawed, and 
afterwards tanned. 

When the skin is to be tanned, it is allowed to lie 
in water for a day or two, to remove any dirt, and to 
wash out the blood; after which it is laid on a round 



TANNING. 331 

piece of stone or wood, called a heam^ and deprived of 
the fat and flesh. It is then put into a pit with lime 
water, and allowed to remain there for some days, 
by which the hair is loosened, and is easily removed, 
by placing it on the beam, and scraping it with a 
blunt knife. As the lime employed in this part of 
the process hardens the skin, it is necessary again to 
soften it. For this purpose, it is put into what is 
called the mastering pit, which contains water and 
dung, chiefly of pigeons or fowls, where it continues 
for some days, the time depending on the thickness 
of the hide. Great care must, however, be taken, 
not to allow it to remain too long, otherwise, owing 
to putrefaction, its texture is completely destroyed, 
so that it is torn by the slightest eflbrt. After this it 
is again cleaned on the beam. 

When the skins are very thick, they are some- 
times submitted to another process. After being 
deprived of the dirt and blood by washing, a number 
of them are heaped together in a warm place, so 
as to cause a slight putrefaction, after which the 
hair is removed, in general without immersing them 
in the lime pit, as this would harden them too much, 
and render the leather liable to crack. They are 
then put into a vat, containing a sour fluid, generally 
prepared by allowing rye or barley to ferment in it, 
by which they are softened, and their pores are open- 
ed, so that they can more easily imbibe the tan liquor 
in which they are afterwards to be immersed. This 
part of the process is called raisings as the hides are 
considerably swollen by it, and also requires particu- 
lar attention, for if too long continued, the skin is 
destroyed by undergoing putrefaction. 

Instead of this part of the operation, which is 
sometimes difficult to accomplish owing to the state 
of the weather, the hides are plunged into a fluid 
composed of sulphuric acid and water, in the propor- 
tion of about a wine pint of the former to fifty gallons 
of the latter, and allowed to remain there till suffi-^ 
clently softened and thickened. 



352 ELEMENTS OF CHEMISTRY. 

The next stage of the process is the tanning, which 
consists merely in soaking the hide in a solution of 
an astringent vegetable, and making this unite with 
the gelatin, by which it is rendered no longer liable 
to undergo putrefaction, insoluble in water, and 
in a great measure impervious to it. The astrin- 
gent substance usually employed is oak bark, procur- 
ed from the trees which are cut in the spring, when 
the sap has risen into them. After being reduced 
to coarse powder, it is put into pits with water, by 
which a solution of the astringent matter is procured, 
called an ooze. In this the hides are immersed for 
several weeks, being frequently turned, to expose 
the whole of them to the infusion, and allow it to 
penetrate them. From this pit they are put into 
others, the liquor bding successively stronger, till it 
is completely saturated. Should the hides be very 
thick, the last into which ihey are put contains some 
of the powder of the bark in alternate layers with 
them, by which, as the infusion becomes weaker by the 
substance combining with the gelatin, more of it is 
taken up, and it is thus always kept of proper strength. 
In this way the skins are allowed to remain, till the 
whole are converted into leather, which is known by 
cutting a small piece from them, and observing its 
appearance. If the process be completed, the cut 
edge is of a brownish colour, but if the tan has not 
penetrated it thoroughly, there is a w4iite streak in 
the centre; of course they must be left in it, till the 
whole assume the brown tinge. The time required 
for accomplishing this, depends on the thiekness of 
the hide. Calves skins take from two to four months, 
and the thick soal leatherhides, from fifteen to twen- 
ty. When this process is completed, the hides are 
removed, and laid again across the beam, where they 
are smoothed, and well beat, to make them more 
solid, and also more flexible, after which they are 
hung up on beams in the drying house, a building 
into which the air is freely admitted, where they 
remain till dry. 



TANNING. 333 

A French Chemist of the name of Seguin, propos- 
ed what seemed to him an improvement in the mode 
of preparing leather, but which has not been adopted 
in this country. It consists in making quickly, solu- 
tions of the oak bark of different strengths, and pass- 
ing the hides through them, beginning with the 
weakest, and ending with the strongest, by which the 
process is considerably shortened. It is said, how- 
ever, that the leather thus prepared is more liable to 
crack, than that manufactured in the usual method. 

It m.a)7 be here remarked, that oak bark contains 
a number of other substances, besides the astringent 
matter, and that, therefore, the quality of the leather 
depends in a great measure on the mode in which 
the infusions are made. One of the substances in the 
bark, is what is called exiract. and which is soluble, 
but not so much so as th.e astringent matter. Skin 
has the power of absorbing this, by vvhich the leath- 
er probably acquires its colour and flexibility ; ify 
therefore, the tan liquor be so made, that it contains 
little of the extract, the leather prepared rnay absorb 
a great deal of the astringent matter, and thus become 
brittle, and more liable to crack. Hence probably the 
cause of that manufactured in the French way not 
being so durable as the other, for, by the m.ethod of 
forming the tanning fluid, much of the astringent, and 
little of the extractive matter is dissolved. Besides, 
v/hen the process is carried on quickly, the outer part 
of the skin only is converted into leather, because, 
this bein^i: speedily tanned, prevents the fluid from 
penetrating any farther. 

The great objects to be attended to, then, in tan- 
ning, are, to procure from the bark as much of the 
soluble matter as possible, and, could some means be 
devised by which the skins could be made to imbibe 
this quickly, a great deal of labour, time, and money, 
w^ould be saved. On this is founded the patent pro- 
cess of Spilsbury , of forcing in the tan liquor b}^ press- 
are. For this purpose the skins, after being cleaned, 



334 ELEMENTS OF CHEMISTRY. 

are stretched on frames, which apply closely to each 
other, but so as to leave a little space between the 
hides. Pipes are connected with these, and the fluid 
allowed to flow into the compartments from a cistern 
placed above them, by which, owing to the pressure, 
it is forced into the hides. It is said, that in this 
w^ay, skins which require a year according to the old 
mode, may be tanned in six weeks, and that some 
may be finished in a few days: it is doubtful, how- 
ever, if the leather prepared is so durable, for, from 
the forcing in of the fluid, the skin does not appear 
to take it in uniformly, so as to tan completely the 
whole of it. 

The tawing of skins, by which they are also con- 
verted into leather, is more speedily accomplished 
than tanning. The skins subjected to this process, 
are those of goals, sheep, lambs, and other thin hides, 
by which glove leather^ and that usually called mo- 
rocco, are prepared. When the leather is to be white, 
it is merely subjected to tawing, but when intended 
to be dyed, it also receives a slight tanning. 

The process followed for preparing the skins, is 
nearly the same as that described. They are first 
freed of the dirt and blood by washing, and hung in 
a room heated by stoves, till they begin to putrefy, 
which is known by their emitting the odour of am- 
monia or hartshorn. During this a slimy matter 
collects on the surface, which is removed by placing 
them on a cylindrical piece of wood, and scraping 
them with a knife, and the hair is at the same time 
pulled oiT. They are next put into a pit of lime 
water, and kept there for some weeks, according to 
their size, by which the putrefaction is stopped, aad 
they become much thicker and harder; and after 
being deprived of the superfluous matter, by scraping 
them on the beam, they are placed in a mixture of 
bran and water, in which they remain for some weeks 
being occasionally scraped. By these processes, the 
whole of the lime and slimy matter is removed^ and 



CURRYING. 335 

the skin is fit for tawing, in ^hich state it is called 
a pelt. 

Tawing consists in soaking the pelts in a warm 
solution of alum and common salt, by which they 
become thick and tough. They are then, after being 
washed, put into a vat with bran and water, and 
allowed to ferment for a short time, so as to remove 
a great deal of the alum and salt, after which they 
are stretched on frames, and kept in a heated room to 
dry. 

By these means, a thin white leather is procured, 
which is made smooth and glossy, by soaking it in 
water, containing the white of eggs. It is then dried 
in a heated room, and the gloss given to it by smooth- 
ing it with a hot iron . 

In the process of tawing/it is supposed that the 
skin imbibes something from the saline matter prob- 
ably aluniine^ by which it is converted into leather; 
this combining with the substance of the skin, in 
the same way as the astringent matter does in tan- 
ning. 

When the leather is to be dyed, as in preparing 
black morocco, after being tawed, it is soaked in a 
sokition of sumach (the seeds of an astringent plant, 
and of course similar in its nature to oak bark.) It 
is then rubbed over with a solution of green vitriol, 
by which it becomes black, the same action taking 
place, as has been already described in the prepara- 
tion of ink, {Seepage 247) ; and after this, it is pol- 
ished by glazing it with a glass ball, or, if required 
to have the ribbed appearance of morocco, by using 
one of boxwood, round which a number of small 
grooves are cut, and by which the roughness is com- 
municated to the leather. 

Currying consists in soaking leather in some oily 
substance, by which it is m.ade more impervious to 
water. For this purpose, the hides, after being tan- 
ned, are soaked in water, and then thinned by scrap- 
ing them w^ith a knife, after which they are rubbed 



336 ELEMENTS OP CHEMISTRY. 

with a polished stone, and well besmeared with oil, 
or oil and tallow. They are next hung in a room 
to allow the moisture to escape, and the oil to pene- 
trate them thoroughly, being afterwards dried, either 
in sunshine or by exposure to heat. 

Shainoy leather is merely sheep or doe's skin, 
prepared as already described, that is, tanned, and 
then subjected to the process of currying. 

It is of the utmost consequence for tanners, and 
others using astringent matter, to be able to judge of 
the quantity of tannin in any article exposed for sale, 
particularly as it varies so much in different samples 
of the same substance, owing partly to the age of the 
vegetable, and to adulteration. Different methods 
have been recommended, but by far the best, is just 
that followed by tanners, but conducted in such a 
way as to be quickly finished. It is well known that 
skins will continue to imbibe the astringent principle 
for many months ; but on a small scale, the whole 
tan may be rem.oved from an ooze in a few hours. 
For this purpose, the astringent matter being ground 
to powder, 1000 grains are to be infused in water at 
about 100^, and after the whole of the tan seems 
dissolved, the fluid must be strained, and the insolu- 
ble matter washed, till the water passes through 
tasteless. A certain quantity of this, say -^-^\h^ is to 
be placed in a bottle, along with some pieces of 
skin, previously washed with warm water, to dis- 
solve the lime, employed in taking off the hair, and 
to remove the loose gelatin ; the skin being dried 
by exposure to air, and weighed before being put into 
the bottle. Leaving them there for a few hours, 
turning them frequently, the whole of the tan will 
unite with the gelatin, and thus converr. the skin into 
leather, so that, by drying it, and w^eighing, we find 
the quantity of tan that existed in the infusion, of 
course of 100 grains of the astringent matter. 

The best skins forthi'^ purpose, are the fresh cur- 
riers' shavings from the strong hides, intended for 



SIZE* S37 

liarness, or ox hides split very thin. They must, 
rfter being treated as above mentioned, and weighed, 
be put into tepid water, and handled for a few 
minutes, to open the pores, and allow them to im- 
bibe the tan. 

Gelatin is procured from different parts of the body, 
these affording different kinds of it, or rather articles 
containing it, but mixed with other substances. 
They are ghie^ isinglass^ and size. 

Glue is procured by steeping skins, bones, flesh, 
and the cartilaginous parts of animals in water ; the 
skins particularly of young animals are considered 
the best. To obtain glue from them, they are soaked 
in lime water, to remove impurities. They are then 
washed, and afterwards boiled, the scum as it rises 
being removed. Alum in powder is next added, and 
the solution is strained, and boiled to the proper 
consistence, the scum as before being taken off. 
When sufficiently evaporated, it is poured into 
moulds, in which it congeals, and is then cut into 
thin slices, and dried in the air. Good glue swells 
when kept in cold water for three or four days ; it 
.should be semi-transparent, of a brown colour, and 
free from cloudiness. In using it, after being broken 
to small pieces, it should be covered with cold wator 
for some hours, to soften it, then boiled till dissolv- 
ed, and again allowed to congeal by cooling. When 
recjuired, all that is necessary is to place the pot on 
a fire, by which the glue becomes fluid. If too thick, 
it must be mixed with a little water. 

Isinglass is the dried sounds of fish, particularly 
of sturgeons, which are caught in great abundance in 
Russia. To procure it, they are merely washed in 
cold water, and deprived of their outer covering, 
after which they are cut into small pieces, and hung 
in the air to dry. Though a much purer gelatin, it 
is not so easily dissolved as glue. 

Sizej the substance used by painters, is prepared 
by boiling in water, pieces of parchment, and of the 
S9 



338 ELEMENTS OF CHEMISTRY. 

skins of animals, and fins of fish, and evaporating the 
solution to a proper consistence. It differs from glue, 
in containing fewer foreign ingredients, and in not 
being so strong. 

The use of gelatin in preparing leather, has been 
already described. It is from the ease with which 
this is acted on by astringent matter, that it is em- 
ployed also for clarifying fluids, either with the view 
of rem.oving foreign impurities floating in the fluid, 
or to carry ofi' some of the substance in solution. 
Hence its use in clarifying cofiee, which contains 
not only an astringent substance in solution, but also 
undissolved matter floating in it. When, then, gela- 
tin is added to coffee, and for this purpose, a piece of 
isinglass or fish skin is used, the astringent matter 
acts on it, and forms a precipitate, by which the cofiee 
not only loses its harsh taste, but the impurities are 
carried down. 

ALBUMEN. 

. Albumen exists nearly pure in the white of eggs. 
As thus procured, it is a glairy fluid, with very little 
taste. 

When kept for some time exposed to air, it putre- 
fies, but when spread in thin layers, and dried, it does 
not undergo any change. When heated to about 165^, 
it coagulates, and forms a white substance, which 
does not become fluid as its temperature falls; shew- 
ing that its properties have been completely changed. 
Albumen is soluble in cold water, and if the quantity 
of fluid be not great, it is separated in its coagulated 
state by heat ; but if the water be about 10 times as 
much as that of the albumen, there is no coagulation. 
Hence we cannot dissolve it in warm water, for when 
put into it, as when a little of the white of eggs is 
thrown into a glass of boiling water, it is instantly 
coagulated. It is also coagulated by acids ; a few 
drops of oil of vitriol added to it, causes instant 
coagulation^ and the same is the case wath spirit of 



MILK. 339 

wine, or even some of the weaker spirituous fluids, as 
wine, which cause a white flaky matter to be deposited. 

Albumen exists in different parts of animals, as 
cartilage, bones, horns, hoofs, flesh, and the mem- 
branous parts. It exists also in considerable quantity 
in blood, from which it is usually procured when 
required in the arts. 

From the properties which it possesses of being 
coagulated by heat it is employed for clarifying 
fluids, as in the refining of sugar, {See page 308,) 
and in many other processes. When used for nice 
purposes, and required in small quantity, white of 
eggs is employed; but for others, particularly on a 
large scale, bullocks' blood is used. When either of 
these is put into a warm fluid, its albumen is coag- 
ulated, and entangles the impurities ; and as the 
scum rises it is removed, so that the whole of the 
foreign matter may be separated, and the fluid is said 
ta be clarified. Albumen acts in the same way also 
in clarifying spiritous fluids. When, for instance 
white of egg is added to wine, or to any cordial, the 
alcohol coagulates it, and the coagulum entangles the 
impurities and carries th'Sm to the bottom. It has 
been mentioned, that both gelatin and albumen exist 
in flesh, and as the former only is soluble in warm 
water, hence the difference in the nutritious quality 
of butcher's meat, according to the mode of cooking 
it. When, for instance, meat is boiled, the greater 
part of the gelatin is extracted, and retained by the 
soup. When, on the contrary, it is roasted, the 
gelatinous matter is not removed, so that roasted 
meat contains both gelatin and albumen, and should 
therefore be more nutritious than the other ; indeed, 
if meat be long boiled, as in making beef tea, what is 
left is not only little nutritious, but very indigestible. 

MILK. 

Milk differs as procured from different animals, but 
*its general properties are the same in all. When 



M(J ELEMENTS OP CHEMISTRY. 

allowed to stand for some time, it undergoes sponta- 
neous changes, and is resolved into its component 
parts ; a thick yellowish substance collects on the sur- 
face, which is crea?n^ and the milk beneath becomes 
thinner than before, and is of a pale bluish colouf. 
When ci'eam is kept for some days without being 
disturbed, it gradually becomes thicker, till at last 
it acquires the consistence of cheese ; and hence one 
method of making cream cheese, merely by putting 
cream into a linen bag, and leaving it there till it 
becomes solid. 

When cream is shaken, it is resolved into its com- 
ponent parts. The process by which this is accom- 
plished is called churning^ by which two substances 
are obtained, butter and butter milk. In the mak- 
ing of butter, cream is allowed to stand for some 
time, during which an acid is generated. It is then 
put into a churn and shaken, by which the butter is 
gradually separated. What is left, the butter milk, 
has a sour taste, but by no means so much so, as that of 
the cream before the churning. Butter is sometimes 
also made from cream which has not become sour, but 
the process is much more tedious, the acid formed in 
the other case favouring its separation. Butter is 
iiierely an animal oil, solid at a natural heat, but held 
in solution in milk, by some of the other substances. 
As thus procured, it is not pure, but may in a great 
measure be freed of its impurities, by washing it 
with cold water ; and though apt to become rancid, 
yet, when mixed with salt, may be kept any length 
of time. 

Milk from which butter has been taken, under* 
goes spontaneous changes. It becomes much sourer, 
and congeals into a mass of the consistence of jelly. 
When heated, the fermentation of this coagulum is 
hastened, and by the Addition of certain substances, 
it very soon takes place ; thus acids and spirit of 
wine curdle it, which is owing to the albumen it 
contains being acted on by them, in the^same way^ 



MILK. 341 

as blood or white of eggs. By far the most power- 
ful coagulator, however, is the substance called ren- 
net^ which is the decoction of the stomach of animals, 
as a calf. When the milk is previously heated, and 
rennet added, it is almost instantly coagulated. If^ 
after this, it is cut, a thinnish fluid oozes from it, 
and if it be put into a bag and squeezed, the whole 
of this is forced out, and a whitish tough matter is 
left ; the former is whey^ the latter curd. On this 
depends the process of making cheese, which varies 
in richness, according to the mode followed in pre- 
paring it. When milk is heated gradually, and 
merely to the temperature at which it curdles, and 
if the curd be freed gently from the whey, it retains 
almost the whole of the cream, which adds to its 
richness and flavour. But when it is curdled quickly, 
and the whey is speedily removed by cutting the 
curd, a great deal, or nearly the whole of the cream 
is carried ofi', and the cheese is poor, and has not 
the rich flavour of that made in the other way. 
The latter is the method generally followed in 
Scotland, where both cheese and butter are got 
from milk, for the whey procured in the process 
yields a considerable quantity of the latter, and hence 
the comparative poorness of Scotch cheese. In 
making cheese, having obtained the curd, and freed 
it of its whey, the remaining part of the process is 
merely to subject it to pressure, by which the whole 
of the whey is forced out, the colour being commu- 
nicated by the addition of colouring matter ; that 
generally used is annotta, which is mixed with the 
milk. 

Whey has a pleasant taste, and contains a conside- 
rable quantity of a sweetish substance, called sugar 
of milk ; hence it is frequently used as drink, and 
from its nutritious quality, it is administered to deli- 
cate people ; hence the use of asses' milk, which con- 
tains a large quantity of it. It is from its containing 
this saccharine matter, that it is sometimes, as in 
29* 



342 ELEMENTS OF CHEMISTRY* 

some of the northern counties of Scotland, made to 
undergo fermentation, by which a very weak spirit- 
uous fluid is obtained. 

BILE. 

BilCj or Gall, is a fluid of a greenish colour, and 
has an intensely bitter taste. It has a greasy feel, 
and is of a thickish consistence, but which varies 
according to the time it has been retained in the gall 
bladder. When mixed with an oil or fatty matter, it 
unites with it, and forms a sort of soap, which is 
owing to its containing soda; hence its use in taking 
out greasy spots, and for scouring wool and cloth, 
and also for cleaning the walls of oil painted rooms. 
Owing to this property also, it is used by painters 
for mixing some of their paints, particularly green 
colours, and for cleaning ivory, the greasiness of this 
being removed by rubbiiig it with bile, by which it 
is rendered fitter for receiving the paint. 



COLOURING MATTER. 

hidigo is perhaps the most important of colouring 
matter^ not only from the richness, but also from the 
durability of its colour. It is obtained from difler- 
ent kinds of plants cultivated in the East and West 
Indies. To ])rocure it from these, they are put into 
troughs, and covered with water and weights, to 
prevent them from floating, and kept at about the 
temperature of S0°, by which they undergo a sort of 
fermentation, the fluid becoming muddy, acquiring 
a green colour, and emitting a gaseous fluid. After 
this has gone on a suflicient time, the water is drawn 
off into another trough, and kept constantly agitated^ 
during _which a quantity of the colouring matter 
separates. Lime water is then added, which is sup- 
posed to favour the deposition, and prevent putrefae- 



COLOURING MATTER. 343 

lion. After the whole of the colour has fallen to the 
bottom, the water is drawn off, and the residue put 
into bags, and allowed to drain, after w^hieh it is dried 
by exposure to air, but kept from sunshine. As 
thus procured, it is a s^ft substance, without taste 
and smell, and generally of a dark blue colour, though 
this varies considerably according to circumstances, 
being frequently mixed with impurities, derived from 
the substances used in its preparation. 

The acids in general dissolve indigo. When oil 
of vitriol is poured on it, a solution is formed, called 
liquid blue^ the colour of which is so intense, as to 
appear black, but when mixed with v/ater, it becomes 
blue. When an alkali, or the solution of green vit- 
riol, is added, they change it to green, and very soon • 
destroy its colour. 

Indigo is used in large quantity as a dye stuff. 
To get it in solution, it is mixed v^^ith green vitriol 
and lime, or with yellow arsenic and an alkali, and 
boiled in water, by which a green coloured fluid is 
formed. These substances, it is supposed, change its 
nature, the indigo giving oxygen to the green vitriol, 
or arsenic, by which it becomes soluble in lime or 
alkali. That this is the case, appears probable from 
the fact, that the colour is changed from green to blue 
by exposing it to the air, so as to allow it agam to 
imbibe oxygen. Substances also diyQd in the solu- 
tion are green, but very soon become blue when 
suspended in the air. 

Logwood contains a peculiar substance, ^vhich, 
v/hen boiled in w-ater, afibrds a solution of a dark 
brown colour, but is altered by the addition of other 
bodies. A few drops of acid change it to yellow\ 
The alkalies, on the contrary, make it purplish. On 
the addition of a solution of alum, the colouring mat- 
ter combines with the earth of the latter, so that, if 
any substance be added by which the earth is precip- 
itated, it takes the colouring matter along with it. 
That this is the case, i§ shewn by adding a solution 



344 ELEMENTS OF CHEMISTRY. 

of alum to the infusion, and then putting in some 
potassa ; the earth and colouring matter are precipi- 
tated, leaving the fluid colourless. 

Some of the metallic salts act powerfully on log- 
wood. Thus, green vitriol changes it to black, and 
a solution of tin in muriatic acid makes it bright red ; 
hence the use of logwood in the preparation of black 
and red ink, as already described, {See Iron and TiUy 
page 247, 259,) 

Jlrnotta^ or Annotta^ is another colouring matter 
much used in dyeing/ It is prepared from the seeds 
of a tree that grows in America. For this purpose, 
after the husks are removed, they are put into troughs 
with water, and beat till the whole of the colouring 
matter is taken from them. The fluid is then heated, 
the scum, as it collects on the surface, being remov- 
ed, after which it is boiled down to the proper con- 
sistence, and dried. The solution of annotta is 
yellowish, and, like other colouring matters, is chang- 
ed by different substances. Thus, the alkalies make 
it much darker. 

It is employed principally in dyeing silks, which 
it makes yellow or orange. For this purpose it is 
always mixed with an alkali, as potassa, which ren- 
ders it more soluble in water. It is also used for 
colouring cheese, being dissolved in the milk before 
it is curdled, and subjected to pressure. 

Litmus^ or Archill is a substance prepared from 
difierent kinds of moss, principally by the Dutch. 
For this the plants, after being dried, and reduced 
to powder, are mixed with potassa and urine, and 
allowed to ferment, by which a reddish substance is 
* ormed, that soon changes to blue. It is then again 
mixed with potassa and dried, by exposure to air. 
Instead of drying it, it is often kept fluid till re- 
quired. The solution of archill is purplish, being 
changed to red by acids, and to blue by alkalies. 
It is used chiefly in dyeing silks and ribbons, but the 
colour is not permanent. 



COCHINEAL. 345 

Madder is another substance employed abundantly 
as a dye. It is the root of a tree, cultivated chiefly 
in Holland, and imported to this country in powder. 
When dissolved in water, it gives a solution of an 
orange red colour, which becomes brighter by the 
addition of potassa, but is changed to yellow b}^ acids. 
When alum is added toils solution, the w^hole of the 
colouring matter may be thrown down. This .con- 
stitutes .the process for preparing lake. For this 
purpose the madder is dissolved in cold water, and 
to the infusion alum is added, and afterwards a solu- 
tion of potassa, by which the earth is precipitated, 
and takes with it the colour, which is then collected 
on a filter, washed, and dried. 

Metallic solutions also change the appearance of 
madder ; green vitriol makes it a clear brown, and 
su^ar of lead brownish rgd. 

Quercitron^ the bark of a tree grovving in Amer- 
ica, is another substance much used by dyers. The 
infusion is of a yellowish brown colour, which is 
darkened by alkalies, and m.ade lighter by acids. 
Alum throws down the colouring; matter of a deep 
yellow. It is also precipitated by muriate of tin^ 
forming a fine lively ^^ellovv. Green vitriol throv^s 
down a dark precipitate, and leaves the solution olive 
green, and blue vitriol forms a yellow precipitate, the 
fluid becoming yellowish green. 

Cochineal is a permanent dye of a red colour, 
derived from the animal kingdom. It is the female 
of a small insect, a native of Mexico, and which is 
merely^ collected on the plants on which it feeds. 
After being plunged into boiling water to kill them, 
the insects are dried in sunshine. The infusion 
is purple, and is changed to reddish yellow by acids. 
Alum makes it become red, but at the same time 
causes precipitation, and on this depends the mode of 
preparing carmine. This is procured by throwing 
one lb. of cochineal, previously ground to powder, into 
10 gallons of water, and boiling it about three hours, 



346 ELEMENTS OP CHEMISTRY. 

after which three ounces of carboiliate of soda, and 
half an ounce of alum, are added, and the whole well 
stirred. Having remained at rest for some time, the 
clear fluid is drawn off, and mixed with the white of 
two eggs, and again boiled. A coagulurv is formed, 
which, when the ebullition ceases, soon falls to the 
bottom. The clear fluid is poured oS", the residue 
thrown on a filter, well washed, and dried. 

Red lake is prepared, by boiling the fluid from 
which carmine has been procured, along with potassa 
and the precipitate formed on the first addition of 
alum. The clear fluid is then drawn off) alum is 
again added, and a precipitate is thrown down, which, 
when washed and dried, is lake. 

DYEING. 

The art of dyeing consists in fixing colours on 
eloths of different kinds, so that they shall not be 
destroyed by exposure to air, or by washing. The 
articles of which cloth is composed, have an attrac- 
tion for colouring matter, but it varies in different 
instances. In some it is so povverful, that the colour 
may be applied without any preparation, except 
merely scouring the cioth to free it from impurities, 
which is usually done with a weak solution of potassa. 
After this, it is soaked in the infusion of the dye 
stuff, which adheres to it, imparting its colour, and 
which cannot be removed by washing. In other 
cases, on the contrary, the altraclion is so weak, that 
though the colour can he imparted to the cloth, it 
is not fixjed ; it is easily destroyed by washing, or 
b}^ exposure to air or sunshine ; but when this is the 
case, it may be fixed by the use of a third substance, 
which has an attraction for both. Thus, if a piece 
of cloth be dyed by madder, it acquires a reddish 
colour ; bu? this is not fixed, it may in a great mea- 
sure be removed by washing; but if it be previously 
soaked in a soluiion of alum, then dried, and after-- 
wards put into the madder vat, it is dyed; and ths 



DYEING. 347 

colour is fixed. This is owing to the attraction of 
the earth of ahim for the cloth, and also for the dye, 
by which they combine, and are thus kept in union 
with the cloth. This constitutes a difference in the 
process of dyeing, and has given rise to the division 
of dye-stuffs into two classes, the substantive dinA ad- 
jective^ attaching to these words, the same meaning 
as in common language. A substantive colour is 
therefore one that will act oi itself ^ an adjective col- 
our requires the addition of some other body. 
Those substances used along with adjective dyes 
have been called mordants^ from the idea that they 
bite in the colour ; they are chiefly alum, and some 
of the metallic salts, particularly those of tin, occa- 
sionally also those of mercury, lead, and iron. But 
these, besides fixing the dye, also change its colour, 
and hence their use in procuring different colours 
from the same dye-stuff, as the remarks on the 
properties of colouring matters show, these being 
changed by the addition of the different agents men- 
tioned. 

From what has now been said, it is evident that 
there are two modes of dyeing, either by substantive 
or adjective colours. When the attraction between 
the cloth and the colour is strong, ail that is neces- 
sary is, to soak it in the infusion of the dye-stuff, by 
which the colour is imparted, and fixed. But when 
the attraction is w^eak, it must be first saturated with 
a mordant, and then with the colouring matter. Of 
course the mordant must vary according to the nature 
of the dye. 

There is still another method altogether different 
from those mentioned ; it is not by using the dye 
already prepared, but by combining the cloth with 
substances which act on each other, and strike the 
colour required ; and in this way also the colouring 
matter becomes fixed. Thus, a piece of cloth can 
be dyed black, by soaking it in a mixture of infusion 
^f nutgalls and green vitriol, the substances used in 



S48 ELEMENTS OF CHEMISTRT. 

making ink, and which form a black colour ; but i* 
this case the colour is not fixed. If, however, the 
cloth be previously immersed in the infusion, and 
after being dried, be put into the solution of ^reen 
vitriol, the same black is produced, the chemical 
action taking place on the clolh, as when the solutions 
themselves were mixed, and the colour is thus ren- 
dered fixed. In this way a great variety of colours 
may be produced. Many of these have been already 
described, when treating of the properties of the 
metals. In dyeing the compound colours, as green, 
this is generally done by giving to the cloth a blue 
colour, and afterwards soaking it in a yellow infu- 
sion. Thus, by dyeing it with indigo, it becomes 
blue, and by putting it into an alum bath, and then 
into quercitron, the yellow of the latter and the blue 
together, form green. 

As mordants are used to fix colour on cloth, it is 
evident, that if, instead of being applied to the whole, 
certain parts only are covered with it, the colour, 
though communicated to the whole, will be fixed 
07iiy on those parts saturated with the mordant ; 
and that this is the case is easily shewn, by making 
some traces with the infusion of nutgalls on cloth, 
and allowing it to dry, and then putting it into solu- 
tion of green vitriol ; the colour, on the traces only, 
will be durable. Hence the mode of appl5nng a 
pattern on a white or coloured ground, and which is 
called calico printings from its being usually done 
on calico. 

Two mordants are in general use by the calico 
printers, alumina and iron in union with acetic acid, 
oracid of vinegar. The attraction between acetic acid 
and alumina is so weak, that they cannot be made to 
combine directly ; but they may be united, and the 
mordant formed, by decomposition, which is done 
by mixing sugar of lead, or the acetate, w^ith alum, 
the acetic acid of the former combining with the 
alumina of the latter \^q form the acetaie of alumina^ 



while the lead is precipitated in union with the sul- 
phuric acid of the aluin ; the mordant is therefore 
left in so-ation, so that, hy filtration, it is obtained 
pure. The iron liquor is procured by puttinj; 
iron filings into vinegar, or rather pyroligneous 
acid, by which it is slowly disi^olved. The solu- 
tions thus formed, are made of the requisite con- 
sistence with starch, to which in general a little 
Brazil wood is added, to give it colour, that the 
traces may be seen when applied to the cloth. The 
instrument by which this is done, is a block of wood, 
on which the pattern is cut. In some places, it is 
interlaid with the felt of hat, which takes up a great 
deal of the mordant when necessary ; and for some 
of the nicer patterns, copper is sometimes used, by 
which the impression is more delicate. The block 
being covered wdth the mordant, is applied to the 
cloth, and struck with a mallet, or forced down by 
machinery, to cause it to leave on as much as pos- 
sible, and by applying it repeatedly, the whole web 
is properly covered with it. It is then dried in a 
stove room, to fix it, and after being washed to 
remove the superfluous part, is put into the dye-vat, 
by which the colour is imparted to the whole of it; 
but by boiling it in bran and water, and exposing it 
on the ground, only those parts previously covered 
with the mordant are coloured, so that the pattern is 
dyed on it. 

By applying different m.ordants to the same piece 
of cloth, different coloured patterns may be produced. 
Thus, if part of a piece of calico be covered with the 
aluminous mordant, another with the iron, a third 
with a mixture of these, and the rest left untouched, 
and afterwards put into a madder-vat, the first wall 
become red, the second black, the third purple violet, 
chocolate, or lilac, according to the proportions, and 
that part uncovered will be reddish, but w^hich, on 
keeping it in brana little fermented, and then exposing 
it on the field, disappears, leaving the ground white. 
30 



350 ELEMENTS OP CHEMISTRY. 

That different colours can be given in this way, is 
easily shewn by a simple experiment. Cover one 
part of a piece of cloth with a solution of prussiate of 
potassa, and another with infijsion of logwood, and 
leave the rest uncovered. When dry, put it into a 
solution of green vitriol, the first will become blue, 
the second black, and the ground will be left white. 

Connected with the art of dyeing is that by which 
bandannas are made. For this purpose, a web is 
dyed Turkey red, and after being laid up in folds, is 
placed between metallic plates, in which are cut 
patterns, similar to that to be given to the cloth. 
Through the holes thus cut in the plates, a solution 
of the bleaching compound [Seepage 221) is allowed 
to flow, by which the colour of that part of the cloth 
is discharged, and a white pattern is left on the red 
ground. 



ELECTRICITY. 

When certain bodies are rubbed against each other, 
for instance, amber or glass upon woollen cloth, small 
sparks dart from them, and they acquire the property 
of drawing light objects towards them, which are 
almost instantly repelled. All bodies do not possess 
this property. If, instead of amber or glass, a metal 
be employed, no effect is produced. The. substance 
first discovered to draw light objects to itself was 
amber, -which w^as called electron by the Greeks, an'd 
hence the origin of the word electricity. Many 
others have since been found to possess the same 
qualitj^, as glass, jet, sulphur, wax, resin, silk, fur, 
and worsted. These are called electrics^ because, 
when rubbed, they excite electricity. Those, on the 
contrary, which have not this property, that is, those 
which do not attract light objects when rubbed, are 



ELECTRICITT. 



351 



called non-electrics ; they are metals, water, and a 
number of salts and earths. 

If, when an electric is rubbed and electricity ex- 
cited, a non-electric be brought near it, the electricity 
is carried off; if, however, an electric be approached, 
it is not taken away, but allowed to accumulate^ 
The former, non-electrics, are therefore said to con^ 
duct it, and hence the division of bodies into conduc- 
tors dJid non-conductors. Electrics, it has been said^ 
do not conduct, while non-electrics conduct; electrics 
are therefore non-conductors^ and non-electrics are 
conductors. To excite electricity, an electric must 
be rubbed, either against another electric, or a non- 
electric The common instrument for this purpose 
is an electrical machine, which consists of a glass 

cylinder, «, which is 
an electric, made to 
rub against a non- 
electric, as a metal 
placed on a cushion 
of leather. The cyl- 
inder is supported 
on non-conductorSj as 
glass rods, b c, and is 
therefore said to be 
insulated ; and at 
each side there is 
placed a metallic cyl- 
inder,/? n, to convey 
the electricity, and 
hence called the conductors. These are also sup- 
ported on non conductors, e /*, that the electricity 
may not be carried off. To the glass cylinder is 
fixed a handle, h. 

Luckily for the science of electricity, air is a non- 
conductor; had it been otherwise, it would be carri- 
ed off the moment it is excited. Most air, however, 
and all objects, whether conductprs, or non-conduc- 
tors, become conductors when moist: hence it is that 




S52 ELEMENTS OF CHEMISTKY. 

during rain, or in crowded rooms, electrical experi- 
nients do not succeed, the air and apparatus being 
rendered so damp, that the moment the electricity is 
excited, it is carried off; and hence also the neces- 
sity of having the machine, and all the apparatus, 
well warmed, that they may not condense the moist- 
ure, and thus become conductors. 

If the electric subjected to friction be completely 
insulated, as is the case with the glass cylinder of 
the machine, the electricity is at first weak, and very 
soon ceases ; but if a communication by means of a 
conductor, be made between it and the earth, or some 
other object, it becomes stron.e:er, and the supply 
may be kept up as long as the friction is continued, 
but it ceases when the communication is removed. 
The machine has therefore a metallic chain 2, sus- 
pended from the cushion^s conductor, n, and touching 
the table, so that it may be in communication with 
some other object. 

B}^ the machine thus constructed, electricity may 
be excited proportionate to its size, and the state of 
the atmosphere ; the drier the air, the stronger it is. 
When put in motion, electricity may be got from it, 
as by approaching the knuckle to one of the conduc- 
tors. 

When electricity passes from one substance to 
another, there is a peculiar odour, a slight noise, and 
a flash of light, which is bright, if the experiment 
be performed in the dark; so that it thus flies off 
from the conductor in sparks. 

That a communication between the machine and 
the earth, or som.e other object, is necessary for 
keeping up the supply of electricity, is shewn by 
removing the chain of communication, i; it is at 
first weak, and soon ceases^ but on again applying 
it, it becomes strong. 

The mostremarkable property of electrified bodies, 
is their first attracting, and then repelling light 
objects. ThuS; if a small cork ball, suspended by a 



ELECTRICITY. 



353 



thread, be brought near one of the conductors, p^ it 
is attracted, and then repelled. It is, however, no 
sooner repelled^ than it is again attracted, again to be 
driven off. In the first instance it receives a supply 
of electricity, by which it is repelled by the conduc- 
tor, and gives it off to the surrounding air. On being 
again attracted, it receives another supply, which it 
as quickly disperses through the air around it. 

Substances electrified by being approached to or 
connected with the conductor, p^ repel each other. 
If, for instance, a person lay hold of one of the con- 
ductors, and stand on an electric stool, which is 
merely a board supported on glass feet, or non-con- 
ductors, by which it is insulated, he becomes electri- 
fied ; the electricity passing from the machine into 
his body, and his hair will stand on end^ because 
each hair, being electrified, repels the one adjoining 
it. The same happens if vv^e attach a bunch of feath- 
ers to one of the conductors; they ore electrified, 
and* repel one another, and the different parts of the 
same feather also repel the others. On this property 
depends the means of measuring the intensity of the 
electricity, v^hich is considered to be in proportion 
to the distance a light object is repelled from the 
conductor. 

It may be considered, then, a general law, that 
bodies similarly electrified repel each other ; if, how- 
ever, two objects be electrified, the one by holding 
it near the conductor, p^ the other near the rubber 
of the machine, n, they do not repel each other as 
before, but approach, evidently shewino; that the 
different parts of the apparatus are in different states, 
which has led to the idea that there are two kinds 
of electricity, one given out by glass, and therefore 
called vitreous^ irovci the Latin word vi/reum, signi- 
fying glass, the other from resinous bodies, and 
therefore termed resinous. Substances, however, 
nccording to circumstances, excite different states; 
thus, glass may be made to give out what is called 



354 ELEMENTS OF CHEMISTRY. 

the resinouSj while the vitreous can be got from 
resins. This led Franklin to suppose, that there is 
but one kind of it, and which exists in all bodies, but 
in very different quantities. Some have equal shares 
of it, some have a superabundance, others a deficien* 
cy. Hence, when two. each having its own share, 
are rubbed together, he imagined that one gained, 
while the other lost it ; the former he said became 
plus^ the Q\\i^rwdniis electrified, signifying that one 
had inorCy the other les^^ than it naturally has. In- 
stead of these terms, vve often speak of a body being 
positively d^nd negatively electrified, the former cor- 
responding with the plus, or having too much, the 
latter with the minus, or having too little. When, 
then, the machine is revolved, the electricity is sup- 
posed to be taken by the glass, a, from the metallic 
matter on which it rubs, n, and is given to the con- 
ductor, _p ; and as there is a chain suspended from the 
rubber, 7^, and communicating with the table, the 
supply is kept up, there being a constant flow towards 
the rubber, from it to the cylinder, and from it to 
the conductor. Hence it is that the conductors, have 
also got different names. That connected with the 
chain, n^ and from which the electricity is supposed 
to be taken, is called the negative, the other, j», into 
which it passes, is termed positivey the former losing, 
the latter having an overcharge of it. From the 
positive conductor, it flies off to the surrounding 
objects with different velocities, according to its sur- 
face. If it be terminated by a point, as when a wire is 
fixed to any part of it, it passes off in an uninterrupt- 
ed stream, as is shewn by approaching the knuckle 
to the wire. But, if terminated by a knob, it dart* 
off in sparks. Thus, when the knuckle is brought 
near the ball, it receives sparks more or less bright 
according to circumstances. The same remarks apply- 
to bodies receiving eledivichy^ pointed ones taking it 
in more quickly than blunt ones. Thus, if the 
fenuckle be approached to the conductor, it receives 



ELECTRICITY. 355 

sparksj but on presenting a wire at the distance of a 
few inches, the sparks cease, the electricity flying 
into the wire. On withdrawing it, sparks again 
appear, but on again approaching it, they disappear. 
Hence the part of the positive conductor, jo, next the 
cylinder, has a number of wires terminated by points, 
and presented to the glass, that the electricity, when 
excited, may be drawn off quickly. 

Though the electricity thus excited may be greater 
at one time than another, according to the size of the 
machine, and the state of the w^eather, when we wish 
it to be very pow^erful, we must have recourse to 
means of collecting it. The apparatus used for this 
purpose, is called a Leydea jar^ so termed because 
it was first constructed at Leyden. It is merely a 
^# glass jar or bottle, a, coated with tin-foil 
I both inside and outside to the same height, 
^^p^c fy^ Through the wooden stopper, c, there 
- ! ,]> passes a wire terminated by a knob at'fif^ 
I and touching the foil in the interior. When 
jT the ball, d^ of the jar is approached to the 

r " J positive conductor, the electricity flies into 
it, but it does not escape to the surrounding atmos- 
phere, or the table on which it is standing; on the 
contrary, it is accumulated, and that it is so is shewa 
by dischar<.^ing i*, which is done by making a com- 
munication between the interior and exterior coating. 
For this purpose a discharger is used, which is 
merely a brass wire terminated at each end by a ball, 
'if X ?/, and fixed at the middle to a glass 
handle, z. Having charged the jar 
by keeping it for some time near the 
positive conductor, the ball, a?, is to 
be applied to the tin-foil, and y to the 
knob, fl?, and the electricity is instant- 
ly set free with a spark, which is much 
brighter than that got from the machine. 
The jar may be discharged in other ways than b^ 
l:he discharger. Thus;> having charged it, if a persori 




356 ELEMENTS OP CHEMISTRY. 

hold it in one hand, and apply the other to the knobj 
the electricity is evolved, and produces when small 
a peculiar sensation in the fingers and elbows, but, 
when large, and fully charged, it passes through the 
chest; indeed it may be made so strong, as to knock 
the person down, or even to kill him. 

When electricity passes from one body to another, 
it travels with immense velocity, and is accompanied 
with great heat. When a Leydeii jar is discharg- 
ed, the electricity travels along its wire, and that of 
the discharger. It might be expected, that as the 
discharger is lengthened, it would require a longer 
time to pass along it; this is not, however, the case, 
at least we are not aware of any difference. Thus, 
if a chain be made part of the communication, being 
fixed to the walls of a room, and at each corner be 
passed through a bladder, full of an explosive mix- 
ture of oxygen and hydrogen, when the jar is dis- 
charged by it, the whole of the bladders are exploded 
at the same instant ^evew though many feet separate. 
For this purpose, the bladders being filled with the 
explosive mixture, are hung by slinngs on nails, and 
the adjoining ends of the chains are put through the 
corks into the bladders to about the distance of }th 
of an inch from each other. Having charged the 
jar, it is placed on one end of the chain and the dis- 
charger fixed to the opposite end. On bringing the 
knob of the one, on that of the other, the electricity 
is discharged, and passing through the gases where 
the wires approach, explodes them all at the same 
instant. 

The discharge of the jar is also accompanied with 
heat, which is often so intense, as to set fire to bodies. 
If, for instance, cotton, besmeared with powder of 
resin, has a spark passed through it, it is kindled, 
provided the machine is in a good condition. 

The discharge of electricity is sufiicient also to 
cause gases to explode. "When hydrogenand oxygen 
are mixed, and heat is applied, there is an immediate 



ELECTRICITY. 



357 




explosion, and the same is the case if an electric 
spark be passed through them. For exploding; the 
gases, a strong glass tube is used, having a wire pass- 
ing in at each side, and terminating in the interior 
at the distance of the yV^h part of an inch from eiich 
other, as in the experiment with the bladders. On 
this depends ihe electrical pistol^ which is merely a 
glass tube, open at r/, and shut at 6, 
with its wires, c d. To fill this 
with an explosive mixture, it is held 
over a bottle, e, containing iron 
filings, water, and sulphuric acid, by 
which hydrogen is set free. By 
holding it a certain time over the 
tube, hydrogen enters, displacing 
part of the air ; a cork is then put 
in at «, and by passing a spark through it, the 
hydrogen and air are exploded. For this pur- 
pose, the Leyden jar being charged, it is put on a 
chain, one end of which is connected with the wire, 
d, holding the pistol by g, in the hand ; c is then to 
be applied to the knob of the jar; the electricity 
flows from the one to the other, and as there is a 
spark passing from wire to wire in the tube, it 
explodes the gasesr 

Such are the principal facts concerning electricity, 
as far as it is connected with chemistry. It is a 
curious fact, that many animals have the power of 
giving an electric shock when they please. The most 
remarkable of these, is the electrical eel of South 
America, and another possessing the same power is 
found on the coast of Britain, and on the shores of 
the Mediterranean. When these are touched, they 
instantly give forth electricity, sufiicient to stun a 
small animal. Electricity is likewise evolved during 
many of the occurrences of nature. The watery 
vapour which arises from the surface of the earth, as 
it is condensed, forms clouds, which become electri- 
fied, and the earth being in an opposite state, if they 



358 ELEMENTS OF CHEMISTRY. 

approach, an electric spark passes between them. 
Electricity also often flies from one cloud to another, 
the one having been positively, the other negatively 
electrified. This is the cause of lightning, and the 
motion produced in the air occasions thunder, which 
is more or less loud according to the quantity of 
electricity, and the distance at which it is heard, 
Dr Franklin made the important discovery, that the 
electricity thus discharged in the heavens, is the same 
as that given out by an electrical machine, which he 
proved by a very simple experimen^t. He elevated 
into the air a kite, from which there descended a cord 
containing a metallic wire, attached to a conductor, 
supported on a glass rod. By this he was enabled 
to charge a Leyden jar, which, when discharged, 
produced the same effect as common electricity. 

Perhaps the' most useful application of our know- 
ledge of the laws of electricity, is the means which it 
has pointed out of protecting buildings and ships 
from being destroyed by lightning, which consists in 
erecting what are called conductors. These are 
merely copper or iron rods, the thickness of which 
depends on the size of the building, fixed to the 
outer walls, reaching to a certain height above the 
highest point, and descending into the earth, a little 
below its foundation, and terminating in a pool of 
water. It has been found that a conductor will pro- 
tect from lightning a circular space, the diameter of 
which is four times the length of the rod itself, meas- 
ured from the highest point of the object to which it 
is fixed. Its height ought therefore to be, taking it 
from the highest part of the building, rather more 
than a fourth of the diameter of the building itself. 

It has been already mentioned, that pointed bodies 
receive electricity much more easily than blunt ones. 
Conductors ought therefore to be terminated by a 
number of points, that they may draw towards them 
the electricity which is discharged from the clouds, 
and a metal ought also to be used that is not liable ta 



GALTANISM. 659 

be affected by the weather. Hence they are general- 
ly made of copper. In fixing a conductor, it is 
necessary to use a substance that is a non-conductor, 
otherwise, instead of defending, it would be the 
means of destroying the building by transmitting the 
electricity through it. For this purpose, it is attach- 
ed to iron staples, but covered with cloth and pitch, 
to make them non-conductors.* Conductors should 
always be made to take the shortest course from the 
top to the bottom of the building, and all the parts of 
the roof covered with metal should be attached to it by 
means of reds, that the lightning may be carried off 
from them.. Ships are also protected by rods or 
plates passing from above the top-mast, along the 
mast^ the lower end passing through the keel into 
the water. 

That electricity will run along conductors, is 
shewn by a very simple experiment. If a glass rod, 
studded with pieces of tinfoil at the distance of the 
10th part of an inch from each other, and having its 
end covered with the leaf, be approached to the con- 
ductor of the machine, the electricity will be seea 
flying along the metal only. 



GALVANISM. 

It has been already mentioned, that electricity is 
excited by the friction of certain bodies. There are 
other means, however, by which it may be evolved, 
particularly through chemical action. 

When two metals, zinc and copper for instance, 
are insulated, that is, fixed on non-conductors, and 
brought into contact, on being separated, the former 
becomes positively, the latter negatively electrified. 
Electricity is also excited during the action of other 
agents on metals; but when this is the case, the 

* A method of" atvaching the staples lo glass has lately been contrived. As Elee- 
tticity passes along the surface only, conductors should not be painted. W. 



S60 ELEMENTS OE CHEMISTRY. 

eff -t:^ '^ilT • '^, >ni those of electricity excited in the 

CO 

": Jvani, an Italian physician, while 
1: ) perforiTiiniX experiments on elec- 

ti Uy discov^efed, that when the nerve 

• L iro^, buspenaecl by a metr^liic hook, 

Vi ^ a metal, it was fnrovvn into violent 

coov .. i -lis naturally excited the cnriosity of 

Galvani, who proved saiisfactoriiy by experiment, 
what had thus been discovered by mere accident. 
From the different experiments which Galvani per- 
formed, he was induced to suppose, that the convul- 
sive n>otions were the same as take place in electrical 
animals, and that the metals served merely as con- 
ductors. He conceived that the diflerent parts of the 
body were in opposite states of electricity, and that, 
on a comm.unication being made between them, it 
was discharged, and caused the convulsions. Hence 
he gave it the name of animal electricity. Others 
have, I'iowever, taken a different view of the subject. 
They suppose that it is merely common electricity, 
and that the animal serves only to show its effects, 
so that it is considered as the conductor. Thus it has 
been showm, that particular sensations may be excit- 
ed in our own persons by a similar contrivance. If 
we take two pieces of metal, say zinc and silver, 
apply one above, the other beneath the tongue, no 
particular sensation is excited ; but if they be made 
to touch each other, a peculiar metallic taste is per- 
ceptible. When, also, we put a piece of zinc between 
the upper lip and gum, and the silver between the 
under lip and gum, and bring them together, a flash 
of light darts across the eyes, provided the experi- 
ment be performed in the dark. Though these dif- 
ferent facts seemed to prove that the effects produced 
on animals by metals were merely those of common 
electricity, this opinion was for a considerable time 
opposed, till, by a particular contrivance, it was put 
beyond the possibility of doubt. It occurred to 



GALVANISM. 



o 1 



Volta, an Italian philosopher, that the convuisions 
might be greater by using more pieces of metal. He 
accordingly took a number of pieces of zinc and 
copper, and arranged them in pairs, putting moist 
cloth between each pair, and following the same 
order throughout, as zinc, copper, cloth, zinc, cop- 
per, cloth, &c. When a communication was estab- 
lished between the opposite ends, by means of vv^ires, 
ah, the effects were much greater than 
^fi when only two pieces were used, and 
he also found, that they were invaria- 
bly in proportion to the number, fully 
/i proving the truth of his opinion, that 

^he electricity was given out by the 

metals, and not by the animals. It has therefore 
been called galvanism, from its discoverer, and 
sometimes also voltaic electricity, and the apparatus 
by which this was proved is now termed a voltaic 
pile. 

Several improvements have been made on the pile, 
the most important of which is placing the metals in 
a trough of well seasoned wood, and covered with 
varnish. This constitutes a galvanic battery. 

The battery consists of a trough, a b, in the sides 
of which are cut grooves, at about the distance of i 




a 





cz'cz 


P 






r 

































s 



or I of an inch from each other according to its size, 
and into which is placed a plate of copper and zinc, 
c z, soldered together, following the same arrange- 
ment as in the construction of the pile, copper, zinc, 
copper, zinc, &c. so that, in looking from one end, b, 
along the battery, we observe all the zinc faces, and 
irom the other, a, all the copper ones, A diluted 
acid IS poured into the spaces between the plates. 
31 ^ 



362 



ELEMENTS OP CHEMISTRY. 



It is not a matter of indifference what metals we 
employ, in constructing a battery ; they must pos- 
sess different powers of oxidation, or of being acted 
on by acids. One must be easily affected, while the 
more the other resists their action the better. For the 
former zinc is generally used ; could gold or silver 
be had sufficiently cheap, they Would answer well 
for the latter, but their expense prevents their use. 
Copper, which is comparatively cheap, and not easily 
acted on, is generally preferred. Different liquidis 
are used for the excitation of galvanism ; that usually 
employed is nitric acid, diluted with about 20 of 
water. When we wish the galvanism to be very 
strongs we rather enlarge the battery than use the 
acid less diluted, because it acts too powerfully on 
the plates, and destroys them.* 

It has been already mentioned, that when the 
limbs of a frog are touched with two pieces of metal, 
they are convulsed. If it be suspended on a wire 
connected with one end of 'a trough, n, and a wire 
from the other, ^, be made to touch it, the convul- 
sions become much more violent. The sensations 



* The annexed figure represents the hnproved form of tlie galvanic battery, con- 
trived by Dr Hare, which he has called a De>1agraLor. It consist of foar troughs. 
a a, b 6, -each 10 
feet long, each tv.-o 
of the troughs are 
joined lengthwise, 
'edge to edge, so 
that when the sides 
of the tvro 6 &, are 
vertical, those of 
the others, a a, are 
horizontal. The 
troughs are sup- 
ported by a frame, 

c c, and turn upon «-— - 

pivots, d d. The pivots are made of iron coated with brass or copper, and a com- 
munication is made between these and the galvanic series within by strips of copper, 
e. The galvanic series of 300 pairs of cooper and zinc plates (connected as in'the 
small cuts, each zinc plate, z, being between tv/o copper plates, cc^) 
k J A n are placed in the troughs, a a.* The acid liquor is ^ 

i / /f ff conlained in llie troughs, h &, and by a partial revolu- ' 

f ( ( ( ^^^'^ ^^ ^^^ apparatus is made to f^ow into the trough 
f« L. I i, J containing the plates, {^cg Jimerican Journal of 
Science, Vol. 3, p. 347.) 




C C 




*The plates are not represented in the lower trough 
in order Uiat the interio!' nia v J13 better undetatood. 




GALVANISM. 363 

excited by the battery are very peculiar. If a ball 
be placed at each end, and the hands, after being wet- 
ted, are put on them, there is a thrilling in the fingers 
and arms, which becomes painful if it be large ; at 
the same time convulsions are excited. It is neces- 
sary, however, for the success of this experiment, 
that the hands be wet, and the greater the extent of 
moistened surface, the more powerful are the effects. 
If, also, we increase the conducting power of the 
fluid, we render them still stronger. Acids are good 
conductors; hence the hands ought to be washed 
with a much diluted acid, as muriatic. If they be 
applied when dry to the balls, there is no effect. 

Galvanism passes through bodies with different 
degrees of celerity. Good conductors of electricity 
iive in general good conductors of galvanism, and 
those which do not conduct the former, are non- 
conductors of the latter. Of course glass, and dry 
vegetable matter, are non-conductors. All fluids, 
charcoal, and metals, are conductors, the last being 
by far the best. 

When the opposite ends of the battery are made 
to communicate, the effects are astonishing; of course 
they differ according to the substances by which the 
communication is established. If a wire from each 
end n p, be brought into contact, there is a spark 
more or less vivid, according to the size of the appa- 
ratus and the strength of the acid, and which is 
renewed each time they are brought together. If, 
instead of using a good conductor, as a metal, we 
employ one of inferior conducting power, as char-' 
coal, the effects are still more brilliant. Thus, if the 
wires be terminated by charcoal, and these are 
brought into contact, the light is very intense, indeed 
so much so, as to be painful to the eyes. 

In the experiments related, light is emitted by 
the substances subjected to the galvanic influence, at 
the same time, however, a most intense heat is pro- 
duced. When -the metallic conductors, up, are 
plp.ced at the ends of the trough, and a communication 



364 ELEMENTS OE CHEMISTRY. 

is established between them, by means of very fine 
wire, as platinum, it is made red hot, the length 
ignited depending on the strength of the battery. 
If a metallic leaf be employed, the heat is sufficient 
to convert it into vapour. This is easily shewn, by 
putting the leaf on one of the wires of the trough, n, 
and having the other terminated by a zinc plate. 
The moment that the plate is made to touch the leaf, 
the latter is dissipated in vapour, being consumed 
with a bright light. Brass leaf burns with a white 
ilame, and red streaks are observed running along 
its surface. Even gold and silver are consumed by 
it, the former burning with a white, the latter w^ith 
a green flame. 

The clDnditions necessary for igniting metallic 
wires on charcoal by the battery are different from 
those which have been recommended for producing 
ils other effects. The ip-nition of these bodies seems 

^ o 

to arise from the electricity passing along them with 
difficulty ; w^hich, as they are perfect conductors, can 
take place only when the quantity to be transmitted 
IS out of proportion to the extent of surface along 
w^iich, it has to pass. It is therefore an object to 
excite as large a quantity of electricity in a given 
time as possible, and for this purpose a very few large 
plates answer better than a great many small ones. 
One of the most convenient methods of constructing 
a battery of extensive surface has been contrived by 
Dr Hare, who has given the instrument the name 
of Calori motor, from the heating effects it produces. 
See Manual^ p. 71. 

The chemical changes w^hich galvanism effects, are 
also very astonishing. It has been already mention- 
ed, w^hen describing the effects of electricity, that 
substances are in different states, some having an 
excess, others a deficiency. The same is the case 
with the opposite ends of a galvanic battery. The 
wire,/?, from the zinc end, exhibits \}(\^ plus or posi- 
tive electricity, that is, the electricity in excess, 




GALVANISM. 365 

while the wire from the copper end, n, sJiew^s the 
minus or negative state, that is, in deficiency; hence 
the distinction of the wires into positive and nega- 
tive^ the former acting by its excess, the latter by its 
deficiency. 

Galvanism is a most powerful agent in causing 
decomposition; by increasing the strength of the 
battery, substances kept together by the most power- 
ful attraction are easily separated. When the wires n 
Pj are introduced into water, it is instantly decompos- 
ed, and a gas arises from each, one being oxygen, the 
other hydrogen. This is easily shewn, by introduc- 
ing the wires into the globular ves- 
sel, a^ by which the gases are dis- 
engaged, and collected in the tube, 
6. That it is a mixture of oxygen 
and hydrogen is shewn by remov- 
ing the tube when full, and apply- 
ing flame; there is an immediate explosion. The 
gases may even be collected separately. Thus, by 
putting the wires into the globular, 
d^ the tubes, h o, soon become fill- 
ed. That in o, immediately over 
the positive w^ire, p, is oxygen, 
and that it is so, is shewn by re- 
moving it, and putting a piece of 
recently extinguished wood into it, by which it is 
kindled ; that in A, over the negative wire, n^ is 
hydrogen, as is shewn by its fhflammability. In 
this instance, there is collected twice as much gas in 
h as in o, water being a compound of two of hydro- 
gen, and one of oxygen. In these experiments, 
there is not only the decomposition of the water, 
but the gases are invariably given off from the same 
Avire, that is, the oxygen comes from the positive, 
and the hydrogen from the negative, and hence it is 
that the wires Ixave been called also oxygen giving, 
and hydrogen giving wires, terms, however, not 
much used. 

31* 




366 ELEMENTS OF CHEMISTRY. 

In the experiment mentioned, it is necessary to 
employ g-o/J or platinum wires. If, instead of these, 
copper ones be used, the result is different, there 
being the disen^^agement of only one gas. Thus, if 
copper wires be put into the globular, «, gas comes 
off only from ?7, and which is hydrogen; the 0x3 gen 
disengaged at the other, enters into union with the 
copper, and converts it into an oxide, because copper 
is a metal which is easily oxidated, while ^gold and 
platinum do not exert so strong an attraction for it. 

In decomposing water by galvanism, the nearer 
the wires are to each other, but without being in 
contact^ the greater is the evolution of gas, and the 
effect depends more on the number than the size of 
the plates. In this respect there is a difference from 
the action on metals. The larger the plates, the more 
brilliant is the combustion of the leaf. The de- 
composition of the water depends also on its purity. 
If pure, it goes on slowly, but if it hold in solution 
any sail, as glauber or sea salt, it takes place much 
more rapidly. If the wires be brought into contact 
in ihe fluid, there is no decomposition, the galvanism 
passing on through the metal without interrup- 
tion. 

The action of galvanism on the compound salts, is 
not less remarkable. When these are subjected to 
it, they are decomposed, and the ingredients collect- 
ed around the different Vv^ires. 
Thus, if a bent tube, a, be filled 
with solution of sea salt, tinged 
blue by cabbage water, and the 
wires introduced at p and 7^, the 
water is at first decomposed, as 
is shewn by the disengagement of gas, but the salt 
itself also very soon undergoes decomposition ; the 
colour of the infusion in r, becomes red, shewing 
that it contains acid, that of §*, becomes green, shew- 
ing that it has an alkali. Here, then, the ingredients 
of the salt are separated, and collected around the 




GALVANISM. '367 

wires in the opposite limbs of the tube, the acid 
being with the positive, the alkali with the negative 
one ; but the wires have not only the power of draw- 
ing the acid and alkali around them, the}^ can cause 
them to pass from one part of the tube to another, 
which also depends on their attracting and repelling 
povver^ Thus, if the wires be removed from the 
tube, a^ and reversed, that is, the positive one, /?, 
put into ^5 and n into r, the infusion will very soon 
change its appearance ; that which was red will 
become green, and the other which was green w^ill 
become red, shewing that the acid has passed from r 
to g^ and the alkali from g to r, having crossed each 
other at a. 

In the above experiment, one tube only is employ- 
ed ; but if more be used, the decomposition may be 
also efiectedj and the ingredients of the salt actually 
made to pass from one to the 
other. Thus, if two tubes, e f^ 
w^ith wires, k /, passing through 
them, be filled with the solution 
tinged blue, and a communication 
7 t ^ ^-~^-^/* ]3e made between them by a piece 
of cotton, c, the moment the w^ires, p n, from the bat- 
tery are connected v/ith the others,, the decomposition 
commences ; the solution in /, will become red, and 
that in ^, green; the whole of the acid, therefore, 
from, e, must have passed along the cotton into/*, and 
the alkali from /, must have gone into e. So that 
the ingredients are collected in separate vessels. 

In these experiments, as with the decomposition 
of water, the wires always draw towards them the 
same substances. Thus, the acid is always found at 
the positive, and the alkali at the negative one. 

What has been said of the neutral salts, applies io 
other substances, as the earthy and metallic com- 
pounds, all of them being decomposed by galvanism* 
It may be laid down as a general rule, that oxygen 
and acids are collected around the positive wire, 






^ 




o6S ELEMENTS CF CHEMISTRY. 

hydrogen, inflammables, alkalies, earths, and metal- 
lic oxides, around the negative one. 

It has been mentioned, that the effect produced by 
galvanic batteries, differs materially according to the 
size and number of the plates ; a different law, 
however, is followed in each case. The burning of 
metals depends on their size, the larger the plates, 
the more brilliant the combustion. Thus, if a batte- 
ry be constructed of a few plates, each having a 
square foot of surface, the effect on the metal is 
astonishing ; but if these be cut, so as to make plates 
of 3 square inches, and the whole arranged in a 
trough the action is but trifling. On the contrary, 
the power of decomposing depends on the nit7nbe)\ 
A few large plates have little effect on saline solu- 
tions, whereas the same, cut into smaller ones, will 
easily decompose them. 

The practical applications of our knowledge of the 
laws of galvanism are as yet not many ; indeed, till 
of late, it was rather as a source of inconvenience, that 
it has been attended to. When a metal is put into 
a fluid, as a solution of salt, there may be no action, 
but if there be two different metals, and in contact, a 
change often takes place, by which one or both are 
destroyed. Thus, if a plate of silver be put into a 
solution of blue vitriol, or sulphate of copper, there is 
no change ; but if along with it, and in contact with 
it, there is also a plate of iron, the salt is instantly 
decomposed, and the copper is deposited on the silver. 
The inconvenience arising from galvanism is princi- 
pally of this kind. The bolts that secured copper 
to the bottom of ships were formerly made of iron, 
which, being in contact, and in a solution of salt, 
expited galvanism, so that they were very soon des- 
troyed, the iron being the metal most easily acted 
on. When, then, pieces of metal are to be immers- 
ed in a saline solution, the same kind ought to be 
employed, that there may be no galvanic action, by 
which one or both may be affected. Accordingly, 



GALVANISM. 369 

ill the instance alluded to, copper bolts, are now 
used. 

Though galvanism has thus been a source of great 
inconvenience, yet the very principle on which it 
proves destructive, has pointed out a means of pro- 
tecting valuable metal from being destroyed by fluids 
in which it is immersed. 

When, for instance, a ship is copper bottomed, 
there is a gradual action on the copper, so that a 
little of it is corroded, and its surface becomes cover- 
ed with a greenish crust, and at the same time, small 
shell fish and weeds adhere to it, which, by increas- 
ing the friction of the water on the vessel, impede 
its progress. It occurred to Sir H. Davy, that by 
putting on pieces of zinc or iron on the copper, 
the action of the salt water would be exerted 
on them, instead of on the copper itself, because, 
these being more oxidable, by the excitation of the 
electricity or galvanism, the action on them would 
be greatest. In this his expectations have been fully 
realized. On a small scale it has been found, that 
copper, with a piece of zinc soldered on it, does not 
suffer any change, when kept in a jar of sea water ; 
and by putting on pieces of the same metal on the 
copper sheathing of ships, the vessels, after long 
voyages, have returned with the copper very little 
corroded. Though copper can thus be protected, 
there is a danger of earthy matter being deposited on 
it from the decomposition of the earthy salts in the 
water, and which would afford a surface for the adhe- 
sion of shells and weeds. This, however, does not 
seem to be the case, when the protectors are of the 
proper size, and when the vessel is in motion. If 
lying in harbour, the copper is apt to be covered 
with weeds and shells, but these are easily remov- 
ed before going to sea. With respect to the propor- 
tion of the protecting metal, it depends in a great 
measure on the size of the vessel, and the velocity 
with which it moves. In the British navy^ about 



370 ELEMENTS OF CHEMISTRY. 

^I^thof iron or zinc has been used. This is perhaps 
less than is absolutely necessary for the protection of 
the copper; but this is not of so much consequence 
as keeping the bottom clean, and which is secured 
by having the protector small. In other vessels, 
about 7 joth and even r^oih has been used, and which 
is perhaps, in the generality of cases, about the requi- 
site quantity. 

The protector may be either soldered to the 
outside of the copper, or nails of iron or zinc may 
be driven into the sides of the vessel, and the copper 
then put on above these, taking care that it is in con- 
tact with them. In steam vessels, the protectors may 
be large, because, owing to the quickness with which 
they move, there is no chance of adhesion of weeds 
and shell fish, and the wear of copper is diminished 
at least two thirds, by using large protectors. 



APPENDIX. 



Table of Capacity of Bodies for Caloric^ compar- 
ed to Water as 10,000. 



Oil of vitriol, 


4290 


Copper, 


1111 


Alcohol, 


6021 


Zinc, 


943 


Sperm oil, 


5000 


Brass, - 


- 1123 


Oil of turpentine, 


4000 


Tin, 


- 704 


Charcoal, 


2631 


Lead, - 


352 


Lime, 


2229 


Antimony, 


645 


Glass, - 


2000 


Mercury, 


- - 357 


Iron, 


1269 







Formula for finding the Volume of Air at differ^ 
ent Temperatures. 

It has been mentioned, {p, 132), that the expan- 
sion of air and all other gases is ^|-oth part by the ad- 
dition of one degree at 32. The volume any quantity 
of air, at any temperature, will occupy when brought 
to any other temperature, is found by the following 
formula. 

Add the number of degrees which the gas is 
above 32, to 4S0. This is the first number of the 
formula. Add the number of degrees which the 
required temperature is above 32, to 480, and the 
product w^ill be the second number. The volume of 
the air at the given temperature, is the third, and the 
fourth will give the volume required. 

Thus, it is wished to know how much 100 cubic 
inches of air, at 60°, would occupy wiien heated to 96. 
60 — 32 = 28 + 4^30 == 508 
9G — 52 = 64 + 480 = 544 
508: 544: : 100: 107.03. 
Suppose the temperature is to be reduced. Thus, 
the volume of 100 inches, when reduced from 75 te 
40 is required. 

75 — 32 = 43 + 480 = 523 

40 — 32 = 8 + 480 = 488 

523 : 488 : : 100 : 93.3. 



372 



APPENDIX. 



TahU of the Quantity of Oil of Vitriol^ and of 
Eeal Sulphuric Acid ^ in 100 parts by weight of 
Diluted Jicid^ at different Specific Gravities, — 
By Dr Ure. 



Oiloi Vit. 


Sp. G,. 


Sui. Acid. 


iJilol Vit. 


Sp. G. 


8ul. Acid. 


100 


18485 


81.54 


68 15760 


55.45 


99 


18475 


80.72 


67 15648 


54.63 


98 


18460 


79,90 


66 15503 


53.82 


97 


18439 


79.09 


65 15390 


53.00 


9Q 


18410 


78.28 


64 


15280 


52.18 


95 


18376 


77.46 


63 


15170 


51.37 


94 


18336 


76.65 


62 


15066 


50.55 


93 


18290 


75.83 


61 


14960 


49.74 


92 


18233 


75.02 


60 


14860 


48.92 


91 


18179 


74.20 


59 


14760 


48.11 


90 


18115 


73.39 


5S 


14660 


47.29 


89 


18043 


72.57 


57 


14560 


46.48 


88 


17962 


71.75 


5Q 


14460 


45.66 


87 


17870 


70.94 


55 


14360 


44.85 


%Q 


17774 


70.12 


54 


14265 


44.03 


S5 


17763 


69.31 


53 


14170 


43.22 


S4 


17570 


68.49 


52 


14073 


42.40 


83 


17465 


67.68 


51 


13977 


41.58 


82 


17360 


QQ,S^ 


50 


13884 


40.77 


81 


17245 


66.05 


49 


13788 


39.95 


80 


17120 


65.23 


48 


13697 


39.14 


79 


16993 


64.42 


47 


13612 


38.32 


78 


16S70 


63.60 


46 


13530 


37.51 


77 


16750 


62.78 


45 


13440 


36.69 


76 


16630 


61.97 


44 


13345 


25,88 


75 


1652061.15 


43 


13255 


35.06 


74 


16415'60.34 


42 


13165 


34.25 


73 


16321 59 52 


41 


13080 


33.43 


72 


1620458.71 


40 


129991 


32.61 


71 


1609057.89 


39 


12913 


31.80 


70 


15975 57.08 * 


38 


12826 


30.98 


69 


16SQS 


56.26 1 


37 


127401 


31.17 







APPENDIX. 




372 


Oil of Vit. 


Sp. G. 


Sul. Acid. 


Oil of Vit. 


Sp. G. 
11246 


Sul. Acid 


36 


12654 


29.35 


18 


14.68 


35 


12572 


28.54 


17 


11165 


13.86 


34 


12490 


27.72 


16 


11090 


13.05 


33 


12409 


26.91 . 


15 


11019 


12.23 


32 


12334 


26.09 


14 


10953 


11.41 


31 


12260 


25.28 


13 


10887 


10.60 


30 


12184 


24.46 


12 


10809 


9.78 


29 


12108 


23.65 


11 


10743 


8.97 


28 


12032 


22.83 


10 


1068^ 


8.15 


27 


11956 


22.01 


9 


10614 


7.34 


• 26 


11876 


21.20 


8 


10541 


6.52 


25 


11792 


20.38 


7 


10477 


5,71 


24 


11706 


19.57 


6 


10405 


4.89 


23 


11626 


18.75 


5 


10336 


4.08 


22 


11549 


17.94 


4 


10268 


3.26 


21 


11480 


17.12 


3 


10206 


3.44 


20 


11410 


16.31 


2 


10140 


1.63 


19; 


11330 


15.49 [ 


1 


10074 


O.Sl 



32 



374 APPENDIX. 

Method of finding the value of Potassa, Kelp^ 
and Barilla. 
These substances are prized for the quantity of 
alkali they contain, either free, or in union with car- 
bonic acid, or sulphuretted hydrogen. As sulphuric 
acid will unite with the potassa in the first, and with 
the soda in the two last, the quantity of this they 
require for neutralization affords an easy method of 
finding their value. For this purpose, it is first neces- 
sary to prepare an acid of known strength, that is, 
one the quantity of real sulphuric acid in which is 
known. This is done by diluting it with water, say 
with 7 measures, and after it has cooled, taking its 
specific gravity. The table given p, 300, will show 
how much real acid 100 parts by weight contain. 
Thus, 100 grains of acid, of specific gravity 1141, 
contain 16.31 of real acid. Now as 100 grains of 
real acid unite with 120 of potassa, and with 80 of 
soda, we have merely to take a certain quantity of 
the article, and having dissolved it, try how much 
of the diluted acid it will take to saturate its alkali. 
Thus, let 100 grains be dissolved in water by boiling, 
filter the solution, and pour on boiling water on the 
filter, till the whole of the soluble matter is taken ofi", 
which is known by its not making litmus paper blue 
as it comes through; next take a measure graduated 
so as to hold 100 grains by weight, and having filled 
it with acid, add it drop by drop to the solution, till 
the litmus paper becomes red, which will show that 
there is an excess of acid, in other words, that the 
whole of the alkali has been saturated. 

Suppose that the acid is of Sp. Gr. 1141, contain- 
ing, as the table shows, 16.31 of real acid, and that 
the 100 grains of the article have taken 97 for satu- 
ration, then as 100 : 16.31 : : 97 : 15.82. 
and as 100 of acid combine with 120 of potassa, then 

as 100: 120 : : 15.82 : 18.98. 
so that the 100 grains of the article contain 18.98 of 
potassa. 



APPENDIX. 375 

The same method must be followed with kelp and 
barilla. Suppose that 100 grains have taken 54 of 
diluted acid, then 

100 : 16,31 : : 54 : 88. 
and as 100 of acid unite with 80 of soda, then 

as 100 : 80 : : 88 : 7. 
so that 100 grains would contain 7 of soda. 

Another method of experimenting, and one by 
which we are more likely to find the average quan- 
tity of alkali, is to put 2000 grains of the article into 
a flask with 12 oz. of boiling water, and cork tightly. 
By leaving them together for three or four days, 
shaking frequently, the whole of the soluble matter 
is dissolved, so that, if 6 oz. be filtered off, we get 
the solution of 1000 grains, and which may be tried 
with the acid as already described. 

In analyzing these substances, as they vary much 
in their composition, it is necessary to take pieces 
from different parts of trie cargo, ail ot which shouM 
be ground to powder, and the requisite quantity 
taken from this. 

Particular attention must also be paid to the red- 
dening of the litmus paper, because it is affected by 
the carbonic acid, or sulphuretted hydrogen, disen- 
gaged from the alkali by the addition of the sulphu- 
ric acid, so that we may suppose we have reached 
the point of saturation, whereas the reddening may 
be occasioned by the gases. This is, however, easily 
known by holding the paper before a fire; if it be 
reddened by them, the original colour of the litmus 
returns, because the gases are expelled ; but if it- be 
by sulphuric acid, it is permanent ; we must there- 
fore add acid till the red does not disappear by heat. 

An instrument called an Alkalunefer is sometirnes used, the 
following: is tlie metliod of using that known as Dr UreV^ — 

Let a tube, closed at one end and of about three fourths of 
an inch internal diameter, and nine inches and a l-alf in length, 
have 1000 grains of water weighed into it ? then let the space it' 
occupies be graduated into 100 equal part?, and everj 10 divisions 



376 A1»PEND1X. 

numbered from above downv^'ards. At 23.44 parts, or 76.56 parts 
from the bottom, make an extra line a little on one side, or even on 
the opposite side to the graduation, and write at it with a scratch- 
hsg diamond Soda ; lower down at 48.96 parts make another 
line, and wrife yotassa : still lower at 54.63 parts, a third line 
marked carb. soda ; and at ^S parts a fourth, marked carh, potass. 
It will be observed that portions are measured off, beneath these 
mark?, in the inverse order of the equivalent numbers of these sub- 
stances, and consequently directly proportionate to the quantities 
of any particular acid, which will neutralize equal weights of the 
alkalies or their carbonati^s. The tube is now completed, except 
that it should be observed whether the aperture can be perfectly 
and securely covered by the thumb of the left hand, and if not, 
or if there be reason to think it not ultimately secure, then it 
should be heated and contracted until sufficiently small. 

Diluted sulphuric acid must now be prepared to be used with 
the tube. When of a specific gravity of 1.141, it will be very 
nearly, if not accurately, of the strength required ; and this may 
be obtained by mixing one part of oil of vitriol of specific gravity 
1.849, with four parts of water. If, when cold, the specific gravity 
of this diluted acid be as above mentioned 1.141, it mustbe nearly, 
if not exactly, of the strength required; but before being admit- 
ted into u?e, shoisld be examined experimentally. Assuming it 
Aiowever as beiog^ absojlitrlj CCrrcCt, it will be found that a quan- 
tity measured into the tube up to any one of the four marks des- 
cribed, is sufficient to neutralize 100 grams of the dry alkali or 
carbonate set down at the mark ; consequently if water be added 
in the tube, thus filled up to any one of the marks, until the 100 
parts are full, and the whole uniformly mixed, one part of such 
diluted acid will neutralize one grain of the alkali or carbonate 
named at the mark, up to which the acid of specific gravity 1.141 
w&s first filled. 

When a specimen of potassa, or barilla, or kelp, is to be exam- 
ined by this instrument, 100 grains are to be weighed out, dissolv- 
ed in warm water, filtered, the insoluble portion washed, and the 
solution added to the rest ; by this process the alkali will be sepa- 
rated from carbonate of lime, or other insoluble matters, which 
otherwise might cause errors in the estimation. The alkaline 
solution is to be put into a basin on the sand-bath, and then the 
tube and acid prepared, For this purpose some of the acid, of 
specific gravity L141, is to be poured into the tube until it rises 
up to the mark indicating the substance to be tested for ; potassa 
or carbonate of potassa for the potash or pearlash of commerce, 
and soda or carbonate of soda for barilla or kelp : then water is 
to be added, until the hundred parts are filled, and closing the 
tube with the finger, its contents are to be perfectly agitated and 
mixed. 

The alkali in the basin is now to be neutralized with the acid 
in the tube. After having once placed the thumb of the left hand 
over the aperture of the tube, it is not to be again removed ; but 



APPENDIX. 



377 



ioverting the tube by turning the hand so that the thumb and 
the mouth of the tube are downwards,' the acid is to be let out 
gradually into the alkaline solution, by relaxing the thumb and 
admitting a succession of small bubbles of air ; the hot solution 
beneath is to be continually stirred, so as to mix the acid instantly 
with the wbole, and the operator must proceed with increased 
caution as the point of neutralization is approached. Very small 
quantities of the ^id may be added, by slightly relaxing the 
thumb so as to permit a minute quantity, less than a drop, to flovy 
to its extremity, and touching it with a glass rod ; the final adjust- 
ment may thu& be made more accurately, than by dropping the 
acid from the lip of the tube. The process must be thus carried 
on, until the alkali is found by the test papers to have been 
exactly neutralized : then the tube must be inverted, the thumb 
removed, drawing its under surface over the edge of the tube, so 
as to leave as much as possible of the fluid that otherwise might 
adhere to it, and having allowed the sides to drain, it must be 
observed how many parts of acid have been used, the number of 
which will indicate the number of grains of the alkali or carbo- 
nate, contained in the 100 grains of the impure alkali operated 
with. 

With respect to the proper strength of the acid it is to be 
examined in the following manner : crystals of bi-carbonate of 
potassa are to be fused in a platinum crucible, the fluid poured out 
upon a clean, cold metal plate, and a piece of th(* resulting solid, 
estimated to be 70, 80, or 100 graip.s, weighed in water ; in 
this way a known weight of pure carbonate of potassa will be 
obtained in solution* The solution is then to be diluted, heated, 
and neutralized by acid from the tube diluted as before described 
from the mark of carbonate of potassa. If it be found that 
as many parts of the acid have been u«ed as of grains of the car- 
bonate weighed out, the acid is of proper strength : if more acid 
has been used, it is too weak, if less has been sufficient, it is too 
strong. Suppose for instance that 100 grains of the salt (fused 
carbonate of potassa) had been used, and that 90 parts of the acid 
were sufficient ; then these 90 parts ought to have occupied the 
iOO, and consequently the 100 parts contain 110th too much 
acid, in consequence of the experimental acid itself containing 
1-lOth more than it ought to do. Hence the latter must be dilut- 
ed with such a quantity of water as will make nine volumes into 
ten, or by l-9th its volum%; for as the 90 parts used are to the 
100 parts they ought to have occupied, so is any number or parts 
by volume of the acid under trial, to the number of parts which it 
ought to occupy. The difference between the two last numbers 
will give the quantity of water in volumes, to be added to the 
acid expressed by the first of them, in order to correct it and 
make it of proper strength. On the contrary, if it were found 
that the 100 parts were insufficient, and that 10 parts more of 
similar acid were required, then there is too much water by 1-1 1th 
of the 77hole in bulk, which would be corrected by adding- 
32^ 



378 



APPENDIX. 



1-lOth of the 35 parts ; hence 0,7 parts by weight of the^same oil 
of vitriol that was used before, must be added for every 35 parts of 
the mixed acid. The correction in any other case may be easily 
made by considering that the number of parts over a hundred 
which are necessary to saturate the 100 grains of carbonate of 
potassa, are proportionate to the quantity of oil of vitriol which 
must be added to bring the experimental acid to proper strength : 
thus if 136 parts of the diluted acid were usedy^hen 36-hundredths 
more of the weight of oil of vitriol already used must be added ; 
and the quantity of oil of vitriol that was added at first being 
known to be l-5th by weight the additional quantity required is 
easily ascertained. These corrections are not strictly accurate, 
but sufficiently so to meet the exaggerated cases put of a diifer- 
ence of 10 parts, and to bring it within the limit of errors of 
experiment. 



APPENDIX. 379 

List of Subjects treated of in this Work^ with 
references to other Books * 



Yov general information ox\ the Articles treated of ia this Work, 
the following books are recommended : 

Murray's System. 
Murray's Elements. 
TH:oiyiPS0N''5 System. 
Henry's Elements. 
Parke's Catechism. 
The account of the articles will be found by consulting the 
Index. 

For fuller information on particular subjects, and such as are 
not contained in the above, consult the following — 

Alphabetical list, with References to the Books in which they are 
treated of. 

THE NUMBERS REFER TO THOSE OF THE CATALOUGE IN P. 385. 

Areometer — 1, 2, 3, 4, 5, 6, 7, 48. 

nderostatics — 1, 8, 15. 

Air— 9, 10, 11. 

Air pump — 1, 4, 12, 13. 

Alcohol— lA, 15, 48. 

Alloys— \4, 16, 15. 

Alum — 1, 14. 

Annotta — 14. 

Archill— \A. 

Arsenic — 14. 

Assaying — 14, 8. 

Atmosphere — 1. See air. 

Attraction — 8. 

Baking — 8, 3, 17. 

Balloon — See aerostatics. 

Barilla — 16, 18. 

Barometer — 1, 8, 3, 4, 13. 

Beer — 8. See brewing. 

Bell metal — 14. 

Bismuth — 14. 

Bleaching — 14, 1,8, 19, 3, 20, 7. 



380 APPENDIX. 

Bleaching by sulphur — 7. 

Blue vitriol — See copper. 

Blowpipe— 1^0^ 8, 16, 15, 33. 

Brandy — 14. 

Brass — 14, 21. 

Bread — See baking. 

Brewing—!^, 22, 8, 23, 24, 3, 48. 

Bronze — 14, 25, 

Butter— I4y 15. 

Calico — See dyeing. 

Candle — 15. 

Carbon — See charcoal. 

Carbufetted Hydrogen — See gas light. 

Carmine — See lake. 

Carron Oil — See oil. 

Cassias, powder of — See gold. 

Cement— 14, 26, 15, 3, 25. 

Charcoal — 7, 27. 

Cheese — 15. 

Chlorine — See bleaching. 

Cinnabar — See merciyry. 

Clay— 21. 

Climate — 8. 

Coal—\A, 27. 

Coal Gas — See gas lightning. 

Cobalt— 14. 

Cochineal — 14. 

Cold— 8. 

Colours — 25, 28. 

Co7nbustio7i—l5, 

Congelation— '15. 

Copper — ^14. 

Corrosive sublimate — See mercury. 

Cryophyrus — 8. 

Currying — See tanning. 

Davy lamp— See lamp. 

Dcrv—8. 15. 

Differential thermometer -^8. 

Distillation— 14^ 3, 29, 15, 48. 



APPENDIX. 381 

Dutch leaf — See copper. 

Dyeing— 14, 1, 8, 30, 31, 16, 3, 28, 20, 7. 

of leather — See tanning. 

Earthen ware — See pottery. 

Elastic fluids — 1 1 . 

Electricity — 1, 8, 9, 3, 11, 5, 6, 32, 34, 35 

Electrometer — See electricity. 

Enamel — 15, 28. 

Etching — 3. 

— .071 glass — SQ, 

Evaporation — 9. 
Fermentation — 14, 16, 48. 
Fire—\lj 37. 

Fire-ivorks — See pyrotechny. 
Fluids, how heated— '31, 
Forsyth's lock — 38. 
Fuel— 31, 
Furnace — 14, 16. 
Fusible metal — See bismuth. 
Galvanism — 8, 6, 36, 39. 
Gas lights— 3, 40, 3S, 41, 42. 
Gilding— 14, 3, 25, 28, 21. 

of iron — See gold. 

GinS, 15. 

Glass— 14, 1, 16, 3, 28, 43, 7. 

, achromatic — 8. 

, etching on— 36. 

, painting on — 44. 

Glue— 14, 16. 
Gold— 14, 

lace — 14. 

leaf— 14. 

Goulard^ s extract — See lead. 

Green vitriol — See iron. 

Gridiron pendulum — 43. 

Gun-metal — 14, 21. 

Gunpovjder — 14, 8, 16, 36, 2S, 21. 

Heating apartmeiits — 43, 37, 45. 

Hydrometer — 15. See alcohol and distillation. 



SB2 APPENDIX. 

Ice^ how got in India — 15. See congelation. 

— 5 Leslie^ s mode of making — 8. 

Ink— 14, 16, 15, 25, 28. 

Ink, marking — See silver. 

Lik, printer^ s — See Ink. 

Indigo,— 14, 15, 36. 

Iron — 14, 8. 

Isi7iglass — 14, page 171. 

Kelp~\S, 8, I, 5, 6. 

Lamp — 8. 

of safety — 8, 46, 15. 

Lake — 15, 43. 

Lead — 14. 

Leather — See tanning. 

Ley den jar — See electricity. 

Lightning — ^See ditto. 

Lime — 21, 18. vol. 3. 

Litharge — See lead. 

Logwood — 14. 

LovVs beads — 7. See areometer . 

Lunar caustic — See silver. 

Madder-^14. 

Malt— 47,48. 

Manure — 8, 16, 15, 26. 

Manganese — 14. 

Massicot — See lead. 

Matter— 2, 11, 5, V2, 32. 

Metals refining of — 14, 16, 9 > 

Metallurgy — 14, 16. 

Meteorology — 8 . 

Milk— 14, 15. 

Minium — See lead. 

Mirrors — 16, 27. 

Morass — 26. 

Morda7its—See dyeing. 

Mortar— 26, 14. 

Muriate of soda — See sea salt 

Music metal — See antimony. 

Nitre— 21. 



APPENDIX. 383 

Oils—ie. 

Oil gas — 8, 14, 38, 41. See gas lights. 
Oil of vitriol, hoiv got — 14. 
Ores J metallic — 14. 

reduction of — 14. 

Orpiment — See arsenic. 

Oximuriatic acid — See bleaching. 

Pe«/— 26. 

Pewter — See antimony. 

Phosphoric bodies — 11. 

Pinchbeck— ^QQ copper. 

Pitch— 14:. 

Platinum — 14. 

Platinum, for giving a light— 3$, 

Porcelain — See pottery. 

Porter — 8. See brewing. 

Pottery— 14, 16, 3, 25, 7. 

Printer^s ink — See ink. 

Prussian blue— 14, 16. 

Pnzzolani— 14, 15. See mortar and cements. 

Pyroligneous acid — 14. 

Pyrometer — 14, 16. 

Pyrophyrus — 14. 

Pyrotechny — 1 . 

Pum — 8. 

Rumford on fire places — 37. 

Saccharometer — 50, 7, 48. 

Sal ammoniac — 14, 8, 7. 

Sea salt — 14, 27. 

Shagreen — See tanning. 

Silver— \4. 

Silvering— \4, 7, 25. 

Size — See glue. 

Smalt — See cobalt. 

Specific gravity — See areometer. 

Soap— 14, 17. 

Starch — 14. 

Steel— 14, S, 15, 7, 38. 

Steam^ heating by — See heating. 



384 APPENDIX, 

Solder — 14. «, 
Sugar — 14, 16. 

candy — 14. 

Sulphuric Jicid^ how got — 14. 

Tallow — See candle. 

Tanning— 14, 16, 1.5, 3. 

Tar—\4. 

Tarras — 14, 15. See mortar and cement. 

Tawing — See tanning. 

Temperature — 14, 7. 

Thermometer— ^ 4, 15, 6, 13, 37. 

_^ Leslie^s — 8, page 332. 

^ register — 8, page 331. 

Thunder— S^e electricity. 

Tm— 14. 

Tinning-— \4 J S, 7. 

Tinsel — See copper. 

Turner^s yellow — See lead. 

Type metal — See antimony. 

Varnishes — 14, 16, 3. 

Vinegar — 14, 

Vitriol, oil of — See sulphuric acid. 

Voltaic pile — See galvanism. 

Wax—\4. 

Water — 11. 

Whisky — 8, 48. See distillation. 

White vitriol — 14. 

Wine—\4, 8, 48. 

Wollaston^s cryophyrus — 8. 

Zaffre — See cobalt. 



APPENDIX. 385 

«/f Catalogue of Books referred to in the preceding 
List, 



1. Encyclopoedia Britannica. 

2. Walker's Lectures on Natural Philosophy. 

3. Jameson's Elements of Science and Arts. 

4. Gregory's Treatise on Mechanics. 

5. Cavallo's Elements of Natural Philosophy. 

6. Hauy's do. do. do. 

7. Parke's Chemical Essays. 

8. Supplement to Enclypoedia Britannica, 

9. Bryan's Lectures on Natural Philosophy. 

10. Gravesend's do. do. do. 

11. Adam's do. do, do. 

12. Ferguson's do. do. do. 

13. Hutton's Recreations in Mathematics and Natu- 

ral Philosophy. 

14. Aitken's Chemical Dictionary. 

15. Ure's do. do. 

16. Chaptal's Chemistry applied to the Arts. 

17. Evan's Miller's Guide. 

18. Transactions of Highland Society. 

19. Home on Bleaching. 

20. Kerr on Bleaching. 

2\, Tredgold on heating Apartments. 

22, Combrune's Theory of Brewing. 

23, Berthollet on Brewing. 

24. Morrice on Brewing. 

25. Handmaid to the Arts. 

2Q, Davy's Agricultural Chemistry. 
27. Bishop Watson's Chemical Essays. 
2S. Smith's Laboratory, or School of Arts. 

29. Smith's Complete Body of Distilling. 

30. Bancroft on the Philosophy of Permanent ColouKS. 

31. Berthollet's Art of Dyeing. 

32. Nicholson's Introduction to Natural Philosopbyi 

33. Berzelius on the Blow-pipe. 

33 



386 a:i?pendix. 

34. Robinson's System of Mechanical Philosophy. 

35. Joyce's Scientific Dialogues. 

36. Biackman's History of Inventions. 

37. Rumford's Essays. 

38. Edinburgh Philosophical Journal. 

39. Bostock on Galvanism. 

40. Peckston on Gas Lighting. 

41. London Journal of Arts. 

42. Accum on Gas Lights. 

43. Smith's Mechanic. 

44. Hooper's Rational Recreations. 

45. Sylvester on Heating Apartments. 

46. Davy on Flame. 

47. Reynolds on Malt-making. 

48. Shannon on Brewing. 

49. Malcolm's Compendium of Modern Husbandry 

50. Morrice on Brewing. 



GLOSSARY. 



ANALYSIS, decomposition produced by chemical 
attraction ; from the Greek anctluo, to separate. 

AREOMETER, an instrument for ascertaining spe- 
cific gravity ; araios^ rarity, metroiij a measure. 

AZOTE, from a and zoe^ without life, as being des~ 
structive to life when breathed. 

B. 

BAROMETER, an instrument for measuring the 
pressure of the air ; barus, heavy, and metron. 

C. 

CALORIC, from the Latin calor^ heat ; a term used 

to denote that agent by which heat is produced. 
CHLORINE, from chloroSy greenish yellow, the 

colour of the gas. 
GRYOPHORUS, an instrument for shewing the 

generation of cold by evaporation, from the Greek 

kruosy cold, and/ero to bear. 

D. 

DECREPITATION, the separation of the particles 
of salts by heat, with a crackling noise • from 
crepito^ to crackle. 

DELTQITESCENCE, salts absorbing moisture, from 
deliquesco^ to become moist. 

E. 

EFFERVESCENCE, the disengagement of an aeri- 
form body ; from the Latin effervesco, to boil 
over, because it comes off with a sort of ebullition 

EFFLORESCENCE, salts losing their water of 
crystallization, and becoming a dry powdery from 
the Latin effloresco, to blow like a flower. 



3SS aLOSSARY. 

ELECTRICITY, derived from the Greek electron, 
because electricity w^s first observed to be excited 
by the friction of amber, called by the Greeks 
electron. 

G. 

GALVANISM, from Galvani, the discoverer of it. 
GASOMETER, from gas^ and 7netron^ a measure, 

a vessel for holding gas, but by which also the 

quantity of gas can be measured. 
H. 
HYDROGEN, from hudor^ water, and ginomai^ to 

generate^ as being the generator of water. 

M. 
MORDANT, a substance used in dyeing, from the 
Latin mordeo^ to bite, from the idea that it bites 
in the colour. 

N. 
NASCENT state, when a body is set free froni 

another with which it was in union ; from the 

Latin nasco, to be born, being as it were just 

brought into existence. 
NEUTRALIZED, when one body has combined 

with another, and the properties of both are des- . 

troyed, they are said to be neutralized. 
NITROGEN, fromm/re, and ginomai, to generate, 

as entering into the composition of nitric acid and 

nitre. 

0. 

OXYGEN, from oxiiSf acid, and ginomai^ to gene- 
rate, so called as being supposed to generate acids, 
by its union with other bodies. 

P. 

PRECIPITATION, throwing down a body in the 
solid form from a fluid ; from the hsiiin precipito^ 
to throw^ down. 



GLOSSARY. ' 3S9 

PYROLIGNEOUS ACID, acid obtained by sub- 
jecting wood to heat : from the Greek pur, fire, 
and the Latin lignum, wood. 

PYROMI]TER, an instrument for measuring high 
temperatures; from the Greek pur, fire, and me- 
iron, 

S. 

SACCHAROMETER, an instrument for ascertain- 

ing the stren2;th oi worts; saccharum, sugar, and 

Tnetron, a measure, because it shows the quantity 

of saccharine extract in worts. 
SATURATION, when a fluid has dissolved as much 

as it can of a solid, it is said to be saturated. 
SOLUTION, the action of a fluid on a solid, the latter 

becomino; fluid ; from the Latin solvo, to loosen. 
SYNTHESIS, combination produced by chemical 

attraction 5 from the Greek syntethemi, to put 

together. 

T. 

THERMOMETER, an instrument for ascertaining 
temperature ; from the Greek therme, heat, and 
metron* 



S3* 



INDEX 



Acetous fermentation, - 

Acetate of lead, 

Acids, - - - 

Affinity, 

Air, - . ^ 

— , how changed by heat, 

sure of - . . 

Air pump, 
x\ibumen, 
i\lcoho], 
Alkalies, 
Alum, 
Alumina, 
Ammonia, 
Analysis^ 
Animal jelly, 

principle?, 

substance?, 



Annotfa, 

Antimony, 

Archil], - , . 

Argill, 

Arnotta, 

Arsenic, 

Atmosphere, 

, pressure of, 

Atmic theory, 
Attraction, 

-, powers modify. 



Page 

300 

166" 

27 

128 

32 

12^' 
33o 
299 

ne 

22^1 
2iM 
179 

2^ 
329 
32^5 
S2e 
34' 
2b9 
344 
224 
344 
287 
128 
128 
57' 

15 



in?, 



-, forces of, 
■, elective, 
-, tables of, 



Fagt 

Bandannas, - - 350 

Balance, hydrostatic - 18 
'barilla, . . 193 

. value of, how found,374 
'2b0 
342 
284 
219 
263 
149 
286 
251 
77 



''^^W metal. 

Bile, 

Bismuth, 

Bleaching, 

Blende, 

Blow-pipe, 

Blue for washing. 

Blue vitriol. 

Boiling point. 



Bone ashes. 
Brandy, 
Brass, 
Bread, 
Bronze, 
Brimstone, 
Brewing, 
Butter, 
milk, 



-, how changed, 78 



Aqua regia. 

Avoirdupois weight, 



63 

47 
46 

172 



Calico printing, 
Caloric, 
Calamine, 
Carbon, 
Carbonic acid, 
Carbonate of Soda, 
lime. 



Carburetted hydrogen, 
Carmine, 



210 
29.9 
263 
311 
260 
163 
294 
340 
340 



348 
58 
263 
152 
169 
192 
206 
155 
345 



INDBX. 



391 



Page 
Carron oil, - - 317 
Catechu, - - 327 
Capacity of bodies for heat, 104 
^ table of, 37 1 



Cassius, powder of, 

Caoutchouc, 

Cements> 

Ceruse, 

Charcoal, 

ChanfifcT?, 

Chemical action, 

Chlorine, 

, how got, 
Choke damp, 
Churning, 
Coal gas, 
Cobalt, 
Cochineal, 
Cohesion, 
Cold, sources of, 
Colnothar, 
Colouring matter. 
Combustion, 



269 
235 
216 



Dutch leaf, 
Dyting, 



E. 



Earths, 
tLarthen ware, 
255 j Efflorescence, 
152! Electricity, 
ll3:Eleutriation, 
5! Evaporation, 
I6I' 
161 
170 



Pagt 
264 
346 



204 
233 
182 
350 
23 
75 



, source of cold, 114 
, spontaneous, 44 



Expansion, 
Expression, 



, uses of, 
exceptions to 



340 
304 
285 
345 
21 
114 

246; Fermentation, vinous, 
342' , acetous, 



F. 



143 Filtration, 
, source of heat, 108 Fluidity, 



Communication of heat, 

Conductors, 

Copal, 

Copper, 

Copperas, 

Corroi-ive sublimate, 

Cryopliorus, 

Crystallization, 

Card, 

Currying, 

D. 

Davy's lamp. 
Decomposition, 

, double, 

, single, 

Decrepitation, 

Deflagration, 

Deliquescence, 

Detonating ball«. 

Differential thermometer. 

Distillation, 

Divisibility, 



86 Fluor spar, 
86 Freezing mixtures, table 
323; of, 

251 'Fuller's earth, 
246 Furnaces, 
266 Fusible metal, 
116 

39 G. 

341 
335) Galvanism, 

Gas blow-pipe, 

Gelatin, 

Gilding, 
157 Gin, 
365 Gluten, 



366 

365 

182 

183 

182 

275 

68 

34 

14 



Glas: 

Glue,' 

Gold, 

Gravitation, 

Green vitriol, 

Gridiron pendulum, (note) 64 

Gum, - - 309 

Gun metal, - - 260 

Gun- powder, - 184 



82 
59 
64 
26 

\ 

291 
300 

- 24 
. 71 

211 

120 

- 224 

lis 

285 



35^ 
149 
329 
272 
298 
3U 
227 
337 
268 
16 
246 



'S92 


INDEX. 






Fag, 




Page 


H. 




Luna cornea, 


277 






Lunar caustic, 


274 


Martshorn, 


179 






Heat, ' - 


68 


M. 




— , capacity of bodies for, 105 








8G 


Madder, 


345 


, quantity of in bodies 


, 103 


Malt liquor. 


293 


-. , radiation of, 


94 


Manganese, 


282 




106 


Marine acid. 


172 


Hydrogen, 


145 


Marking ink. 


274 


. lamp, 


151 


Massicot, 


254 






Mastich, 


323 


I. 




Matter, 


13 






Mercury, 


264 


Ignition, 


84 


Metals, 


236 


Incandescence, 
Indelible ink, 
Indian rubber, 


84 
274 
325 


^w>nn rsT 


242 
237 
339 


fiTTiflnfinn df 


,, UAiUcttlUll VJl, 

Milk, 


Inflammation, 


143 


Minium, 


254 


Ink, 


247 


Mirrors, how silvered. 


267 


Iron, 


242 


Mordants, 


347 


Isinglass, 


337 


Mortar, 


214 


<• 




Muriate of ariimoaia. 


198 


K. 




^f ^^A^ 


195 
172 






Muriatic acid, 


Kelp, 


193 






• , value of, how found, 


574 


N. 




Kino, 


327 










Neutralizatioiij 


181 


L. 




Neutral salts. 


181 






Nitrate of potassa, 


183 


Lac, - - - 


323 


Nitre, 


189 


Lake, 


345 


Nitric acid. 


167 


Lamp black. 


155 


Nitrogen, 


142 


Lamps, - . - 


109 


Nitro-muriatic acid. 


172 


of safety, 


157 


Nitrous acid, how got. 


167 


Latent heat, 


72 






Lead, 


254 


O. 




Leather, 


330 






Legivation, 


23 


Oils, 


314 


Ley den jar, 


355 


Oil of vitriol. 


173 


Light, 


120 


Olefinnt gas, 


159 


Light giving apparatus, - 


107 


Oxygen, 


139 


Lime, 


205 




139 


-, now goT, 


Litharge, 


254 


Oxymuriate of lime. 


221 


Litmus, 


344 


Oxymuriatic acid, 


161 


Lixivium, 


- 33 


Oxy-hydrogen blow-pipe. 


149 


Logwood, 


S43 


Orpinjent, 


288 



I2<rBBX. 



39$ 





Page 




Page 






Silica, 


- 226 


P. 




Silver, 


273 






Silvering, 


277 


Paris plaster, 


209 


Size, 


337 


Papin's dis^ester. 


781 


Smalt, 


285 


Pendulum, gridiron, (note] 


64 Soap, 


315 


Percussion lock. 


202,' 


Soda, 


177 


Petrifactions, 


2091 


Solution, 


31 


Pewter, 


263 


Specific gravity, 


17 


Phosphorus, 


164 


' , changed 




Pinchbeck, 


263 1 


by heat. 


62 


Pitch, 


324 i 


Spectrum, 


122 


Platinum, 


280 1 


Spirit of sea salt. 


172 


Porosity, - - - 
Potassa, 


14 


trr',nr\ 


299 
34 


177 


Spontaneous evaporation. 


, how got, 


177 


Starch, 


310 


Precipitation, 


48 


Steel, 


244 


Prussian blue. 


249 


bugar. 


307 


Prussiate of potass, 


249 


, of lead, 


256 


Pulverization, 


. 22 


Sulphate of iron, 


246 


Putrefaction, vegetable, 
Pyrometer, 


302 
70 


-|;^^„ 


900 


Sulphur, 


16S 


Pyroligneous acid. 


302 














ing. 


165 


Q. 




Sulphuric acid. 


173 








17*1 


Quercitron, 


345 


, now got. 


1 #o 

fJ7^ 


Strength of. 


fJ 4 ^ 

164 


R. 




Sulphurous acid, 


164 






Sympathetic ink, 


286 


Real2:ar, 


288 


Synthesis, 


27 


Radiation of heat, 


94 






Red ink. 


259 


T. 




Red lead. 


254 






Refraction of light. 


122 


Tan, 


327 


Reaumeur's porcelain. 


232 


Tannin, 


327 


Register thermometer, 


70 


Tanning, 


330 


Rennet, 


34! 


Tar, 


324 


Resins, 


322 


Tawing, 


334 


"Retort, 


36 


Tests, 


55 


Rum, 


- 299 


Thermometer, 


67 






HifTf-rf^nf i'^1 


fiR 


S. 






67 






70 


Safety lamp. 


156 


, regisiei, 
Tin, 


257 


Saltpetre, 


183 


Tinned iron. 


259 


Sanctorio's thermometer. 


67 


Troy weight, 


16 


Saturation, 


32 


Turner's yellow, 


255 


Ship protectors, 


369 


Type metal, 


289 



3M 



INBEiK. 





Page 


Page 


' V. 




Watery fusion, - 42 


Vapour, 


8S 


Wax, - - - 313 


, condensation of, 


82 


Whey, . . 341 


Variations of temperature, 


106 


Wine, ... 292 


Vegetable bodies, 


291 


White lead, - - 255 


Vegetable principles, 


307 


White vitriol, - - 262 


Vinous fermentation, 


291 


Woulfe's apparatus, (note) 38 


Vermillion, 


265 




Volatile oils, 


320 


Z. 


Voltaic pile, 


361 




W. 




^inr, . - .261 




Zaffre, - - 285 



Water. 



147 



6 6>7(D' 



UBRARVOF 




'VMY 



M 



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lifi 



m. 



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